it gone a bit stale since invasion ended, and HHH won the undisputed title from jericho and merged it to one title.
It was stale a bit before that to be honest.
The invasion was awful, it had so much potential and they well and truly screwed it up. The main problem was that everyone knew Vince would win and he wouldn't let WCW even get one hint of victory in there. It was basically a storyline to well and truly kill off WCW, and it worked.
For a start, why stick ECW and WCW together at the invasion? ECW and WCW's heat against each other was really well known as WCW poached a lot of ECW's stars (Raven and Mike Awesome for examples). It would have made sense to keep ECW as a seperate thing, or heck leave them out entirely since not many "average joe" fans knew of ECW.
Remember the feelings you had watching the original nWo form in WCW? For the first year or two of the nWo angle it was brilliant! The angles, the swerves, you just didn't know what was going on and they made it feel like a true invasion.
Nash and Hall highjacking Nitro and bullying the announcers, run ins on matches. Hogan joining them, attacks on WCW's "owner" (Nash powerboming Bischoff off the Nitro stage!).
WCW was at it's peak right then, and you'd have thought WWE could have at least borrowed some of the nWo invasion angles with the WCW invasion... it just flopped, end of story :-/