If you watched him at Sunderland, it wasn't glimpses. A few of us here used to watch Sunderland and discuss his games. He was a consistent game changer after the first few weeks of getting to know his teammates.
I'll be honest, there was a tiny bit of doubt as to whether he'd be able to do it in the PL, but it was clear he was at least miles better than Antony.
The loan to Rangers was a farce. I believe Gerrard was the one who got him in and then promptly left?
Either way, he did very well his first game or (may have even scored), then if I remember correctly, Van Bronkhorst threw him into the Old firm derby away, he had a poor game in a match where Celtic completely outplayed Rangers, and after that, he was out in the cold and only played if there was absolutely no one available.