I used to play it quite a lot until my old video card fried while in League of Legends( my advice, don't ramp up the detail, it will murder your top of the line card, no joke, keep the settings low). I especially loved the variety of the classes and they way they could be used to work with each other. I kinda hated the really cheap classes, like the ones that have near permanent stun. But they've probably balanced the classes over the last year a lot better.
In the end, it all comes down to team play. If your team, as an element, gets along well and plays well, you will win. But if there one guy, that one guy, that does everything in his power to get himself and yourself killed, it's just about game over.
My recommendations for characters, if you want a great tank/damage dealer try Mordekaiser. If you want a really cheap, easy to play, ranged damage dealer, go for Ash, Morgana is a great support character, also Heimdinger and his sentries is fun.
Also, don't call it an RTS, it about as RTS as Diablo. And again, keep the video settings low.