Okay. First of all, it is totally okay to judge a game based on gameplay alone. Especially when that game is a game about gameplay. Which DOTA2 is. DOTA doesn't have a narrative or a message; it's closer to a sport, so it's all about gameplay.
The game is on Source so it will probably run on your PC. If you can run TF2, you can probably run DOTA2.
I may be wrong, but I believe DOTA2 will be free to play. Since the original game was a mod, I imagine the developers will release the game on Steam for free and use it to boost Steam's library of F2P games and thus increase membership and Steam saturation. But I look forward to being corrected.
Also, LOL is a DOTA clone. It would be like saying "I think CS: Global Offensive will have a strong initial following, then people will go back to Modern Warfare". The people that play Counter-strike or DOTA are totally different groups of people than those that play CoD or LOL.
Faye, if you don't like the look of the RTS stuff, try Savage 2. It's the same concept but you play in first-person on the ground. It's F2P, although I haven't played it in a long time so it might be barren by now.