I loved some of the goals he scored for us, and he was also a brilliant finisher... except when he wasn't.
Whether he lived up to expectations or not is a tricky one because of just how big and crazy the hype was when we signed him - it was unfair. I think it was easy to believe he was a different sort of player to what he actually was (youtube was in his infancy back then and I remember I could only find about 2-3 clips of goals he scored for Southampton up to that point). We were basically told we'd just secured the next Thierry Henry, guaranteed. Seemed to take a long time before we got to see him play properly, too. I remember one of the first glimpses we got wasn't even for Arsenal, it was a substitute appearance for England in the last 5 or so minutes of the game. He didn't get involved much but I remember him bringing a ball down very well about 25 yards out and fizzing a brilliantly-struck half-volley which the keeper had covered fairly easily in the end, but the technique was perfect. I remember thinking in that moment we had a player on our hands.. (I was only a year older than a very young Theo Walcott myself..). Anyone remember the 2 goals he scored against Germany in the under 21s game? I remember seeing those and thinking 'wow', the pace was unreal and the finishes emphatic, very Thierry Henry-like.
Overall I always liked Theo and he was very much part of a period of Arsenal's history (06-11) that, despite the fact we won fuck all, were often seen as bottlers/a soft touch and a few players I loved turned out to be bellends, I look back on very fondly tbh.