Difficulty just seems to be higher in some rooms/encounters because the harder ones are practically designed to rape you - mages set up so they'll slap you around with fireballs, almost killing your mages with one hit, stuff like that. This situations only stay hard when there's no way to pull with caution, e.g. setting up simple ambushes by putting your party on either side of a doorway and having your tank pulling.
As soon as mobs have to get to you, not the other way around, it's not hard anymore, because enemy mages die just as easily as yours - and practically every white/normal mob is a oneshot for a good equipped/skilled rogue or damage-warrior anyways. In big fights with one boss and many adds - just tank the boss and have your party kill off all the adds first instead of wailing on the boss and eating damage from 5+ other enemies at the same time.
A couple of fights really only are hard because the game forces you to walk right into it - like in one of the back alleys in Denerim: even if you set up your guys far away and have just your tank walk up, there's a little cutscene and after that your whole party is set up just so the mobs can rape you. Or, also in Denerim, one encounter where via script a falldoor is closed, probably trapping half your party to be eaten. In cases like that it helps to have Morrigan cast sleep/waking nightmare/mind blast.
Anyways, maybe I'm just awesome

But "normal" really feels... normal. It's not an easy walkthrough, but it's not frustrating hard either. If some situation seems to just casually stomp over your party, it's either just bad luck as I've already mentioned in an earlier post, or you need to stop and think for a minute how to approach the situation differently. Maybe take a ranked mob out of the fight in some way or wait around the corner and pick the mobs off as they run after you. I still find the game very fun and manageable even with Wynne in the party camp 90% of the time. It's actually easier in some cases, because without a dedicated healer you can deal more damage and/or crowd control
