Yup, lots of mistakes. Black should have won this one, and White missed a few better moves.
After 4.c4 Black could play 4...Nf6 instead, so if 5.cxd5 Nxd5, then 6...e6.
After 7.Bb5, instead of 7...Bh4?!, perhaps better is 7...Bf6 or 7...Bg4 and 8...Nf6.
8.g3 may be OK, but I might have played 8.Nxh4 Qxh4+ 9.g3 to get rid of the active Black bishop and get Black's queen out early.
9...Bxc3?! looks weaker than the developing 9...Ne7 move.
12...Ne4? doesn't look good as it takes away the protection of the Black bishop and loses control of the center. Black should castle and get his king protected.
Now, instead of 13.c4?!, best is 13.Ne5!, threatening 14.Nxg4 and 14.Nxc6. The moves may be 13.Ne5 Bh3 14.Nxc6 bxc6 15.Bxc6+ Kf8 16.Rd1 and White is a pawn up and has a better position.
13...Bf5 doesn't look the best. Perhaps 13...Be6 to control the center and protect the d-pawn.
15.dxc6 does not look like a great move. I would have given it a blunder. Best seems 15.Qc3! Nxf1 16.dxc6 and 17.cxb7.
After 15.dxc6?? Rxd3 16.cxb7+, now Black plays 16...Bxb5! and after 17.bxa8=Q Qxa8, Black is crushing White, who is a queen down.
17.Rd1? looks bad. Best seems 17.bxa8=Q Qxa8 18.Bxd3 Nxf1 19.Ne1 with an unclear position.
17...Rb8? is no good. Black should play 17...Bxb5 and be a piece up.
18.Ba6? looks weak. White should play 18.hxg3.
19...Nxf4?! isn't the best. Black can play 19...Nxc1 20.Raxc1 Bxa6 and come out ahead with an extra piece.
20...Qb6? is weaker than 20...Bxa6 21.Rxd8 Rhxd8, and Black is still winning.
21.Re1 may be OK, but 21.Bxd3 Qxb7 22.Bb2 looks stronger for White.
21...Kd7?! exposes the king too much. Perhaps 21...Kf8 22.Bxd3 Rxb7 is better.
24.Qxb7? looks too slow and no counterplay for Black. Perhaps 24.Qh6, threatening 25.Qxh2+ is the better continuation.
25...Rhe8?! may be bad. Black does not want to exchange pieces. Perhaps 25...f6.
Rather than 26.f5?!, stronger seems to be 26.Rac1, threatening a discovered check and winning a major piece.
26...Rbd8? may not be the best, although Black is trying to stop the threat of 27.Bf5, pinning king and rook. Perhaps 26...Rbc8 or 26...Kd7.
27...Kd8?? is the final bad move that loses because of the White knight forking king and queen. Black had to play 27...Kd7, and if White plays 28.Ne5+, then 28...Ke7, aiming for 29...Kf8.
This game has lots of mistakes. Seriously. There are too many mistakes to count (although I suppose that the maximum would be 58). I am posting this game because, especially in live chess, people take the ratings too seriously. Play new openings and it leads to interresting positions where your opponent is more prone to make blunders. NN had 200 points higher than me and by playing novelties I was able to go up 3 minutes on the clock (it was a 10 minute game) and stump him somewhat. Comments are awesome!