The Total War franchise revolutionized the RTS genre. They are the only game to do what they do. Most RTS's are very similar. Build harvesters, gather resources, build troops, fight. However Total War is different. No gathering resources, fighting is different than the move-attack feature most RTS are plauged with. The real-time battles are a lot of fun to play. Using different tactics with chariots, cavalry, heavy spearmen, elephants, etc. The only draw back, while you can hop on for a half hour only, you won't get a lot done. I've played Rome and Medieval II for hours on end and only gotten a fraction of what I wanted to do. Xfire says I've played 77 hours for Rome and 240 for Medieval. I've beaten Rome once, and "beaten" Medieval a couple times. However each faction is totally different and a new experience every time. Each Faction is guaranteed at least 50 hours minimum to complete the objectives for victory, however to conquer the known world.. 100+.
If you get a Total War game, you'll have it for a long long time. Especially if you only intend to play it in 30 min intervals. On the other side, it is a genre of itself. And I enjoy Rome more than it's expansions (Barbarian etc), however when it comes to Rome or Medieval, it's a draw. Each have their pros and cons. Medieval has the experience in design from Rome and the 15 other expansions/games, however Rome is the original. If you get Rome tho, I suggest getting the patch to clear up a few bugs and such. Once I get my new laptop and can run Empire: Total War (the newest one) I'll let you know how that is. I'm anxious to get that puppy running.
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*looks at his vast selection of RTS's*
As for other RTS's. I've really enjoyed Empires: Dawn of the Modern World. It's like the generic RTS's that I described above, the only thing that I think sets this one apart is the different eras you can play. From the Medieval age to Gunpowder, Imperial, WWI, and WWII. I'm a big history fan so being able to play all the eras of history is exciting. Plus it's fun to have a tank attacking bowmen

(only if you allow the settings to). Also the campaigns are fun. There are a couple for each era. I'm really disappointed that my CD isn't working anymore.
Company of Heroes is good to. It's one of those revolutionary type of RTS's IMO. However as far as I know, there is no way to mute the vast swearing. Only way I got around it was turning off the volume. There might be a slider to mute the voices however, I'm not 100% sure.
I'm playing StarCraft right now. That is always a fun one. As for WarCraft III, I'm not a big fan of the 3D cartoon-ish graphics. And I think the heroes totally ruin the game. Plus the computer seems insane with the "zergling" rushes. It's nice, but I'm not a big fan of it. However, I'm crediting WarCraft II to the start of my official gaming career back when I was like 8. My uncle had it and I would look over his shoulder and play when he wasn't. I love that game even today and I deeply miss it. Blizzard really made me mad when they took out the naval part of WarCraft. I would encourage WarCraft II over III because I feel Blizzard lost its roots. Not exactly sure how that works, but WarCraft III just doesn't seem like the WarCraft I grew up with. The new classes with heroes and spells and no navy.. that's lame.
Total Annihilation is another old school RTS that I have always enjoyed. Unfortunately it might be impossible to find.. it's that old. For Windows 95

. But it's always nice to make robots fight each other. Xfire says I've played 14hrs of Total Annihilation, but I've played for much more than that before I was using Xfire. Lots and lots of units, land, sea, and sky. Both sides, Arm and Core, are basically identical, just different skins and rate-of-fire really.
A cheap $10 one that me and my brother like is Stronghold: Crusader. Build your castles, train your men, build your city (bakeries, flour mills, cattle farms, etc.), and fight of course. It's a laid back game that isn't flashy or in-depth. After maybe a month of light play it'll go on the back-burner, but it's a nice cheap game to hold you over and come back to after a while. There have been many a times I with I hadn't let my friend borrow it indefinitely.
Star Wars Empire at War is a unique RTS. The different types of battles are fun. Space and land. I haven't played it in a long time because I got over after a while. There was a couple things about it I didn't like too much but it was fun while it was fun

. The main thing I enjoyed was the Star Wars theme, and the space/land battles. Nothing like having a Star Destroyer blow apart a Rebel Cruiser and then invading the helpless colony.
Alright, I think that's enough for you. There are a couple other ones that I could probably tell you about. But you can ask me personally

. Hope it helps!