Freakin' epic.
Aizen is hilariously pathetic when he's rationalizing in a panic.
"I can't sense your Spirit Pressure, you must not have any or exchanged it all, it's not because you're way stronger than me!"
"Look at that, my Zanpaktou is disintigrating! That must mean I'm evolving so I don't need it! It's certainly not because I'm fucking dying!"
What a tool.
Anyway, so Ichigo lost his Shinigami powers eh. I know the series doesn't end here, so it seems fairly obvious that he's going to have to further develop his Hollow powers. If Nel teaches him to become an Arrancar, he can at least get a new sword, so there's that at least.
Plus, he will get his Shinigami powers back at some point, because Isshin clearly isn't powerless. And one assumes he's used the FGT at one point.
I imagine he had to use the Getsuga Tensho because, even though he was much stronger than Aizen, he wasn't doing any real damage to Aizen in return. Every time he hurt him, Aizen just regenerated, then evolved even further. The FGT was likely his attempt to put Aizen down for good.
It seemed obvious to me at least that if he didn't put Aizen down hard, Aizen would just keep getting stronger until he DID surpass Ichigo.
What else was he supposed to do? Just slash at Aizen ineffectually all day? Even though he was stronger, he wasn't DOING anything to Aizen.