That's interesting, because I had the opposite experience. The encounter building tools in 4E were so great that I spent maybe an hour preparing for an adventure's worth of combats, and the combats tended to be more dynamic and interactive than encounters I do in other games.
Older editions of D&D, by contrast, had me spending an hour or so per combat, which added up to a dozen or so hours per adventure, just selecting and statting up the bad guys. The difference is night and day. I far and away prefer 4E for the ease of prep, the ease of throwing together an encounter ad hoc, and the ease of creating custom baddies and custom situations to challenge my group.
I suspect the difference is largely one of playstyle; I tend to tailor encounters to challenge both my players and characters. Others prefer a more freeform system of random or mostly random encounters, where some battles may be a walk in the park where others are extremely difficult. To each his own, and where 4E had fewer tools for the sandbox style, it was an evolutionary leap for the tailored challenge style.
I suppose this is where I add the obligatory hope that the 5E designers will note what each previous edition did best and give us a game that does everything they all did, but better.
Play what you like, of course!
Hi - yes, creating encounters in 4e is quite easy and good fun. It was not hard in pre-3e though; it became too hard in 3e because all monsters were statted like PCs, so they were too complicated to create or modify using the RAW. NPCs also were very complex - I shudder when I look at the lone example of a statted NPC in my Pathfinder core book.
I find 4e works well for a game with 1-2 big encounters a night, where you know in advance what those encounters will be. Other editions work better for exploration and sandboxing.
Eg my Monday 4e game we had 1 large fight in 2.5 hours of play, the 8th level PCs defeated Koptila the undead Ogre King and destroyed the Necro-energy Monolith, then initiated a coup against the Bandit King of Llorkh.
In the Pathfinder Beginner Box game the previous Wednesday, in 2.5 hours the 2nd-4th level PCs, after a uncomfortable night in the home of a strange old woman they could tell was not human, went to Castle Caldwell to clear it, and ploughed through around 15 assorted encounters with various monsters and NPCs.