Bottom line, just enjoy the game. Almost everyone has 50% winrate. The only exceptions are the very top (0.01%+). Even the pros have 53-57% winrate.
That's how MM works. This is same in Starcraft 2, LoL, HoN or any games that employ advanced MM algorithm.
If it wasn't 50/50, where would the wins come from? For every winner, there is a loser. Not everyone can win all the time. I remember I was on a 9 game winning streak. Then I lost 14 games in a ROW. That's at least 10-14 hours of pure misery in a whole week.
I currently have 1191 wins, 1189 loss.
Winrate is NOT an indication of skill (biggest misconception of pubs). You could have someone else who has same wins/losses and belong in a low tier. You move up MM rating by winning matches you're supposed to lose (you're lower end player out of 10) and earn rating.
Of course there's no way to tell what matches are favored against you. Valve hid that to avoid flaming and deter poisonous behavior. For example, Heroes of Newerth (another Dota clone) has rating number visible to everyone next to your name. People are already fighting before the match starts (GG IM CARRY, YOU SUCK, BUY WARDS ETC).
Here is more info on ELO.