I think Oasis briefly 'had it' and then 'lost it' in a coke fueled snow storm and have struggled ever since. Thing is, Liam is at once an asset in his rock-front man mode, but a liability in that you feel that any attempt by Noel to do something a bit different or experimental will be met with "I'm not fookin' singin' that fookin' shite!"
Plus, in basic terms - The tunes just aren't as good as some of them once were.