Disclaimer : Instead of cleaning the backyard, I am here. Forgive the longish post (how ironic).
I couldn't get through Kato and Ken , because there's one point where I just keep getting warped backwards in the game.
I beat Monster Lair the other day and it kind of got on my nerves a bit, because it is a tad repetitive. Also Chris Bucci's review mentioning the amount of stages made me think it's gonna take me forever, but it surprised me with ending sooner then expected.
Like many games of a bygone era, Monster Lair is "on the long side", but that is a complaint that can be leveled at countless games, so it is hardly damning. Monster Lair's awesome (IMHO) soundtrack and excellent execution (I feel that the mechanics, controls, stage design, etc. are well-polished) make playing and re-playing the stages (even the earlier, familiar ones) a pleasant experience. Stage 3 is one of my favorites in the game, despite being such an early level, because you can race through with a wonderful fluidity (yes, you have to destroy all the huge boulders to be a true master).
General advice to avoid tedium: To keep things entertaining, I suggest folks adopt my "Grab every single power-up and fruit philosophy". True, you won't use any given weapon for more than a second. You won't have more than a few moments to relax, since you're constantly taking care of business. Plus, it forces you become comfortable with all of the weapons. Even on bosses (except for a few that still scare me), I'll go into battle with any weapon. It keeps you on your toes, especially if they are short range or very weak.
The mini-stage (flying dragon shoot-em-up) prior to the bosses could have been shorter, but, hey, it's only a minute, IIRC, so it's really not that bad. But I understand that folks find this segment a bit tedious...
I still can't remember all the crazy warps and secrets in Kato & Ken. Re-visiting games is somewhat frustrating, because I have to re-discover so much crap: I feel like an old fogie who's going senile. To put a positive spin on things: at least this senility allows me to get more enjoyment out of the game. I suppose I'd be bored by half the games I play if I remembered everything. Thankfully, I haven't seen a deterioration in my motor skills
Bottom line: SENILITY improves REPLAY VALUE. Truth. ON CHANGING PERSPECTIVES: I re-gained an appreciation for JJ & Jeff over the years; I like it far more now than I did in 1990 (when I thought it was somewhat lackluster and decidedly NOT "next-generation" caliber).