I think it took slightly under an hour when I did it.
Like you say, it's not that it's difficult - it's just that you inevitably make silly mistakes. Especially with the gravity puzzles near the end.
I got right near the end a week or two back, with two puzzles left and had only used 3 lives.
Went nice and careful...
Died once on the last-but-one puzzle. Screamed. Succeeded on that puzzle with four lives gone.
Remembered exactly what I need to do on the last bit. Steadied my nerves. Tried it. Died. Shouted some more. Stuffed a towel under each armpit. Tried it again, and got the achievement. Then put the sweaty tea-towels back in the kitchen.
Had two quick goes on worms last night, but wasn't feeling it. I liked Worms back in the day, and was okay at it - though I was not one of those who mastered the ninja rope to the degree they could get out of a tiny nook on one edge of the screen, whiz around the full map, drop dynamite onto an enemy's head, and get back to the relatively safe place where they started all in a few seconds.
Some of the new (to me, at least) weapons are great, though. The holy hand-grenade, the banana bomb, and the exploding sheep were always fun, and continue to be, but this is the first I've seen of the concrete donkey, the herd of buffalo, and a few others - all of which have had me laughing out loud (and cringing as I invariably cause more friendly-fire damage than enemy damage).
edit: typo