I don't think anyone is disputing that first season, which was really impressive. Based on that alone you are bound to have fond memories. Personally I was at St Andrew's every week so I saw just how good he was.
It's the ignorance and denial towards the rest of his time here, and the defensiveness from some people who want to pretend he never missed the penalty (or that it doesn't matter) that tends to fuel the counter argument really. It probably wouldn't be necessary, but as has been mentioned, we have some rewritten history here, because after a second season which was just about average, he was here for another two and was very poor. I can recall some people here getting very upset about it when it kept getting highlighted, but it is just the facts. It is almost unique to have a player so good at one point, and so bad at others over such a spell, but for the majority of the time he wasn't good enough in the end.
On the flip side, I do know where you and others are coming from. You are sentimental about him and therefore largely unable to look at the overall picture. We should collectively wish him the best though, he's obviously had a lot to deal with having those injuries which must have also been hard mentally, and I hope he can have a great future with whatever he decides to do.