It's still useful for ganking but it now requires a more coy approach, not obnoxiously teleporting infront of your enemies majority of the time.
Before it's nerfs, it could be blatantly used to instantly break up a fight, or completely turn the tides of a fight. Teleport on CC intensive champions was a bit too strong, considering the range of a great deal of CC is in the game. On a different note, it was becoming stale and a bit toxic even viewing pleasure. You would be expecting a good fight to start, and instead of anything happening once an initiation began, a teleport forced everything to draw to a stalemate OR it would completely tip the balance of the game with one Summoner Spell. All in all, it boiled down to who had the ability to use it best, which locked out non-mobile champions quite often, not to mention other spells.
In my opinion, it is still useful for ganking, just not in such a way that it was used for previously. Just being able to get within roaming distance is fair enough because you don't HAVE to engage the instant Teleport is used. You can simply use it save traveling time and wait for an opportunity. Time spent waiting on the said opportunity would still be less than the time it would take to get into position without teleport.