What bothered me about this wasn't that monsters were dangerous, but that even 'slow' monsters were often faster on the attack than I was.
It looks like 4e is going to bring back a bunch of attacks each round for "solo" monsters (Case in point: see this excerpt from Worlds and Monsters about 4e dragons).
I can understand the desire here. When a group of PCs fight a single big monster with one attack/round, it isn't always as exciting as it could be.
In the ridiculous/epic/gestalt/Greyhawk/Ragnarok campaign, we fought one of these guys. Go look at it. Be sure to check out the picture. See those little things flying around it? Those are huge white dragons. Anyway, this fight should have been a lot tougher than it was... but big, sentient glacierthings don't get too many attacks... so we took it down pretty quickly.
Really, though, the answer isn't to give it more attacks or to give it immediate reactive attacks or something like that. The answer is...
Well, go back and look at the thing. The answer is pretty obvious:
- How the hell do you attack it? Unless its name is Achilles, stabbing it in the heel isn't going to do much good. Really, stabbing it at all isn't going to be much more effective than someone eight inches tall stabbing you with a needle. It might hurt, but it will mostly just be annoying.
- You and your party-mates charge the thing. You have the party tanks on either side of you. The great beast claws you... but not the guys standing 5' to either side of you... despite the fact that its hand is the size of a bus?
Make it so that you have to get into position to be effective. You might have to climb the thing (see Shadow of the Colossus). You might need to find the loose scale (see The Hobbit). There are all kinds of possibilities.
Area effect attacks: big things should hit big, not fast.
Note the combination of these two things can make for an exciting fight. PCs need to get in position to attack, but they want to stay spread out so that they don't present an easy target. When you have area-dependent buffs or touch-dependent healing, this adds to the tactical considerations. Fighting a big thing should be different.