I have started playing in the internet recently and playing microstakes. The reason is that I wanted to avoid loosing too much in the beginning. Now, after ~15 evenings I am losing a bit more than wining but the difference is not high. But I see that I don't have a big motivation in playing micro. Is there any differences in opponent skills when playing on higher level?
You state you don't have much motivation playing micro stakes. I understand from your statement that what motivates you is the money gains. They are indeed low at micro stakes. And every poker player would be happy to rank 1st at a tourney with a million dollar gain. But what should motivate you is the game itself. If you see the game as a part time time job to make extra income you won't succeed. And you'd better learn another skill you can trade part time for money (build websites, sell food, sell home made handcrafts etc...). If you are passioned about poker and focus on your game, play your A-game, as a result you will win (variance considered), and money will juwt follow. You could try to play $1000 buy-in games, or $5/$10 CG, you would be playing with players who also lure the big money prizes, but who are very experienced and know what they do, and so going ITM would be much harder. Playing such higher stakes would be even more frustrating for you because you would lose much more money. If you don't have any motivation playing micro stakes, it is likely you won't have any playing higher stakes.
You should play Poker for fun and with what you can easily afford. Harvey's right - don't expect to make significant cash amounts. I personally just like winning, the money comes second!
the players will be better at the higher stakes. holdem has a huge variance. do not move up until you can beat the small game for at least 8bb/100. the higher your win rate is, the lower your variance will be.