There's both pluses and minuses...
The gameplay in itself was amazing. I loved doing all the sidequests and main quests, and I cried a lot while playing - like the cure of the Genophage and Mordin's death. The cutscenes were epic.
However, I was most disappointed with the ending. I'm not saying I hate it - I ended the game with sacrificing myself for the synthesis ending since I played my whole 3 games with a 100% paragon and being nice to the Geth. It was a good ending - the only things that bothered me were the destruction of the relays and the inconclusive end scene. It never explained what happened after the relays were destroyed - who else survived and what they did after the Reapers were defeated. It never told us what our Love Interest did after Shepard died.
In conclusion - this is an amazing game that I love to play and replay - I would just like to know what happened after and to see some modifications in the character creation to make Shepard not so... Snape-like...