I liked him late in the game because of his change from local bully (he was the Nelson (from "The Simpsons") of the Zelda series) to a huge help in the Imprisoned battles and even tried to keep Zelda from Ghirahim's final plan. Even though he failed there, he still tried to redeem himself when he caught Zelda back in the past. And in the end, after you destroy Demise, you can see that he accepts Link and Zelda being together.
At the beginning, I wanted to push him off a cliff, if it weren't for the fact he's just call his Loftwing I might've. I definitely preferred the 'land below' Groose, still cocky, but he at least had enough sense to realise they were in trouble and he should help.
Groose on land is my dawg. After the second fight with the imprisoned, he quickly rose to not only my favorite character in SS but one of my favorites in the Zelda series itself. I was SO thankful for that catapult. Not to mention he becomes a completely respectable character by this point in time, recognizing both his place and Link's in the adventure. After proper tantrumming (not a word) he sucks up his Personal feelings and makes himself useful. Groose is one of the new things I've been hoping for in the Zelda series, a third Person with distinctive Personality and is useful. Link and Zelda finally have a third whose Personality wasn't too similar too theirs (unlike Midna who was still considered a sidekick and even if she wasn't, she became very much like Zelda). I hope to see more like Groose in later Zeldas.