If I were to place my finger on what is eating time up it is all of the tactical miniature elements. I move here, I miss causes him to shift etc. Which are interesting, however they do take time to implement.
I've always used minis so I can't judge that really. But I do know that once you have the minis thing down (especially GM and the maps), and everyone knows the 4e rules as well as they knew their previous game rules, it will speed up. We use to get through 1-2 combats per ~4 hours of gaming. We can get through 3 now, so for us it seems to have gotten faster.
Also, with the increased HP it feels like this endless attrition. My wizard (that died last session

) needed at least four hits with his 1d6+4 damage at-will power to kill a 30 hp kobold.
Wizards don't seem to be optimized to take down solo opponents with at-wills (or in general) They are optimized to do good damage when taking into account AOEs. So while it took you 4 hits to drop one kobold, often if you had AOE you might drop two in the exact same time, or if you're lucky, 3

Strikers and fighters output good damage especially early on relatively speaking. At-wil for rogues can reach over 30 in one hit. Slap your strikers for not taking out your kobold faster

I can't say it was any better in 3.5, with all spells being DAILY, I often had to manage my good spell use to the boss fights, and if I was foolish enough to load up on damage spells, it was torturously slow for me to take someone out (and costly). It was generally better to do things to help everyone else take them out faster (haste, sleep, web, clouds, glitterdust, etc.) At higher levels, I think with more encounter/daily's, you'll be leaning on at-will damage less. Just a guess.
I dont mind the extra hit points, but it also seems that damage has dramatically decreased from previous incarnations of the game. Damage needs to be increased for all characters except possibly the ranger who seems pretty solid. What has your experience been with this?
Was your GM using minions? It seems that if minions are used for some percentage of the opponents, they of course die in one hit no need to even roll damage. Then the other opponents do take a little longer, but that should even out as a result. Wizards are supposed to be good minon killers, if you haven't been running into a lot of minons, you may be feeling it's uphill for you, because in effect, it is. Kobolds are no longer all "minons". They have tough guys too. If your GM throws all non-minons at you, then yes, you'll be in for a ride.
Some of what you're experiencing may also be your group composition and their choices. Bad choices at later levels do less harm. bad choices at those early levels can have a huge impact on overall performance. You'd know better there though.
Hope some of that is relevant.