Ok, I've spent about 10-15 hours with this game, so I'll give my initial impressions. I'll put as much info here as possible, since I plan to play this a lot and hope interested parties join in.
First, the bad...
Battle System
As I expected from reviews, the battle system is definitely the game's weakest spot. I think the main problem is the weird mix of being able to run around freely with an "active time" battle system. You can run right up to someone, but can't attack until the little circle fills. It's even worse when you're equipping heavy armor like I have on, because your guage fills more slowly. Also, for some odd reason...you can melee attack an enemy, then run 10 feet away, only to be melee attacked from a distance. It's odd, and really gives you no motive to try to dodge attacks. One last complaint is a lot of the large enemies have a ton of HP, which is fine in and of itself. But, right now I'm at a point where a few of them are no danger to me...but it still takes me 5 minutes to slowly wittle them down while they hit me for 1 or 2 hp. Ultimately, I often find myself basically standing there just waiting for the circle to fill up. Not very involving just yet.
Caveat to add to the above:
Bear in mind I haven't played for that long and I tend to explore more than normal on maps; I'm over-leveled for where I'm at. I also know that stuff gets harder. I wouldn't mind a 5, 10, or even 20 minute fight if I was actually being challenged. I'm thinking I should put all of my folks in lighter armor - take a little more of a beating and get a faster-paced attacks going. I just figured out how to work with combos last night, which let you do a lot more damage (up to four attacks in one). So, I don't think the problem is nearly as bad as I'm reporting - I'm just doing a lot less damage than I should be, which is making the fights longer. Also, I have my avatar's build set up as more of a tank/paladin (short sword + shield, healing), so I'm not exactly spec'd for DPS. Lastly, in the single player, you can summon the knight for most of the larger enemies, which really helps take them down much faster.
Probably the only other bad is that a lot of mechanics aren't explained very well. For example, combos are very, very easy to set up...but no where does it tell you "hey, why don't you set this and this up as a combo and try it!" in the story. I guess modern games are starting to rub off on me, and I should've just referenced the book. Not really a huge negative, just thought I'd mention it.
Now, the good (which I think far outweighs the bad):
Difficulty
The single player game is mostly easy, but fun. Again, I'm not super far in, but what I've seen so far (and read from others' views) is that it's typical JRPG faire, which is just fine by me. The online quests can be very tough, and require a well-coordinated team to beat unless you're a lot higher level than the enemies...which is good in my book.
Graphics
I think this game is beautiful. The environments often look photo-realistic in a lot of ways. I often find myself just stopping to enjoy the scenery. Also, it's more than just high-res textures, things just look very pretty. In battle, the animations and enemies are great, Trolls/Treants/Bosses (and who knows what else) are HUGE, and it just looks very nice. Think ~2 stories tall. It's very fun to bust out that giant knight to go head to head with those huge beasties.
There is also an in game Crystal Camera that you can use to capture the scenery and save it to the hard drive.
Here's one of the opening trailers. Looks very nice in hi-def:
http://www.youtube.com/watch?v=9DhVHJKAxc8
Skills/Magic
There are eight areas to specialize in: short swords, long swords, elemental magic, bows, spears, axes, divine magic, and staves. There are enough skill points to max 2 tiers, or 3 after rebirth (explained below). Or, you can go for one and snag passive skills out of the rest. Lots of different ways to go, and totally open. In the single player story, I'd just recommend having a relatively well-rounded party.
Rebirth: When your avatar reaches level 50 and you complete the game (which will come before 50, I believe), you can "rebirth", which basically drops you to level 35 and gives you back all of your spent skill points, plus 40 extra skill points your first four times. You can rebirth and respec as many times as you want, you just only get the bonus the first four times.
Items/Equipment
There is tons of equipment to be bought and found. From the newbie stuff I've seen it looks pretty good, graphically. You can equip any weapon...but skills are tied to the six weapon tiers above, so you won't really be wanting to swap around very much.
You can upgrade a weapon's strength by adding materials, which is nice. Also, there is a system in place for binding new weapons from old weapons + some materials. I haven't gotten into this yet, but had a ton of fun doing this in past Level 5 games (Dragon Quest 8, Rogue Galaxy).
Online
Ok, so yeah...the thing you actually asked about...online play. I would say that all of the things above add up to an above-average game. The online portion is great.
First thing to know is that online, you play only with your avatar character that you design when you start a new game. The single-player story is mostly about Leonard and others while your avatar is just along for the ride. I really kind of like that set-up...because many games that have you create a custom from scratch character end up telling no story at all, with no likeable characters. You just have a lifeless shell that you created for your battle style.
You can hop online once you unlock GeoNet (the online service). Really it's just a few hours into the game. The online quests take place in explorable areas from the single player game. Pretty much standard go here/do this/kill this type things, and the maps are pretty big. The few I've done have taken about 20-30 mins. Once you sign in to GeoNet, it's very easy to hook up with other players. I just use an option "find players close to your level" and it gets me into someone's town (more below) with a group doing quests at my level. You can also add people as friends in-game (don't have to be PSN friends), talk over text or voice chat, etc. Completing quests gives you items and Guild Rank which allows you to unlock tougher quests as it increases.
There are new quests coming each week (until June, I believe), so overall should be a lot of variety. From what I have read, getting platinum on this game will take 600-1000 hours...so there is plenty of online playing to do, although that would involve a lot of repeating quests, I'm sure. I'm planning on at least playing until I've hit most maxes, not sure if I am going to get 10m guilda, buy every item in the game, etc. I'll probably be shooting for hitting 50 S-rank quests, though. So, I guess the nice thing is that there is a lot to do...so if other folks pick this up we could be doing a lot of playing together.
Online - Georama
If you've played Dark Cloud 1 or 2, you might recognize this term. Georama is the mode where you get to build your own town. The more money and time you sink into it, the grander it'll be, selling higher level goods. You get a discount in your shops. Other players can visit your town and shop or meet up to head out on quests. You can also unlock a lot of special armor sets and other really high-level stuff.
Here's a vid showing some town-building:
http://www.youtube.com/watch?v=PM1jUSRX1X0
Bottom line is...the game isn't perfect, but between questing, binding items, building up a village, etc...there is a ton of fun to be had playing the game on or offline.