I believe the two games I've played the most recently are Braid and Portal, both very similar in gameplay. Neither seem to care much about time (?), and both are essentially series of extended brainteasers. I wonder what it means for complicated games that both of these have been exceptionally popular.
Braid is wonderful. I finished the first three worlds in a single sitting, and finished up four in spare time today. Where Portal has the tongue-in-cheek Skinner box environment, Braid seems, strangely enough, to have a more serious, complete plot. I'm somehow exceptionally invested at this point in finding out if there's a princess and what happened to Tim. I'm not sure I'll stay as engaged, but the painting, music, context in the pre-level books, and even the house and starry night all play perfectly.
I'm not sure I liked the overly overt Donkey Kong homage, though the Super Mario Bros tributes have, overall, been well done. I'm looking forward to finishing. I've only had one occasion so far (in Finicky Follower or whatever it is when the key follows you rather than lets you take it) where I've figured out the trick, but had the solution play out incorrectly. That is, I figured out how to get the key where I needed it, but somehow managed to make it fall by grabbing it too early, yet still left of the ladder (which should make sense to those who have played, but not too much for those who haven't). It, intuitively to me at least, should have worked where I made it all happen. I wasted 20-30 minutes looking for another answer before giving it another shot. Poof.
Compared to other games, that's still an excellent ratio.