Mega Man 5 is in roughly the same position as 4 was to 3, with a flatter difficulty, fewer energetic enemies, and a general lack of hard platforming until the end. The main trend among all the main stages is to let the player approach everything at their own speed and take down each enemy one by one. They do have their moments, like these.
However, take a look at some of the tougher sections from Mega Man 4.
These put the player in a situation with some momentum, either by physically moving the player forward or making them unwilling or unable to stop due to enemies or unstable platforms. Mega Man 3 did this with Spark Man's vertically moving platforms and Gemini Man's gauntlet of dragonflies and fish, while Mega Man 2 had Air Man's clouds, Heat Man's vanishing blocks, and the unforgettable lasers in Quick Man's stage.
Some of that may have been a little too much, and this specific type of difficulty isn't always necessary for a good platformer, but those sections where the player has to make a series of quick decisions or die have always been the heart-stopping moments that will be remembered later, and Mega Man 5 is lacking in this category.
What remains is a mix of decent enemy encounters, a handful of neat stage mechanics of varying quality, and a lot of nice-looking fluff.
The boss fights and weapons are also a let-down, with the bosses roughly equal to Mega Man 4's selection and the weapons largely unnecessary. However, the Super Arrow has a lot of potential for players who know what's ahead, and Beat is useful enough to make a good reward for finding the letters. Also, the fact that the charge shot is lost when hit goes a long way toward balancing it.
As hidden extras go, the letters were a good decision. In Mega Man 4, there's a part of Pharaoh Man's stage I always miss because getting the Balloon takes you to the midpoint, and this is a common issue when games include split paths with one "correct" choice. Hiding the letters in plain sight or a small side room avoids that problem.
The end stages fared a little better, with some nasty enemy combinations, new ideas, a more lethal version of Dust Man's pistons, and a great deal of tiny platforms over pits, as though the designers finally remembered what had been missing and tried to cram it all in at the end.
Unfortunately, the Dark Man idea was a terrible mistake. Only the third puts up a respectable fight, with the rest falling easily into "lamest boss of the series" territory. Wily and the bosses leading up to him are solid enough, but they can't fix the bad taste left by Dark Man.
I feel pretty comfortable calling this the weakest entry so far, but even so, Mega Man's basic gameplay is strong enough to keep it from being a bad game. It still retains some of the fun and charm that hooked me on the series, a few of its ideas (such as the gravity switching and bubble platforms) are pretty neat, and Dark Man is the only thing I would consider outright unpleasant about it.
I was going to have a post about some specific enemy placements before this, but I've decided to wait until after Mega Man 6 so we can look at everything the main NES series did.
However, there's one more thing I wanted to call attention to that didn't fit with the main posts.
With one sad exception, Wave Man's stage does not have a single thing to shoot at outside the Ride Chaser segment, which throws up a massive red flag in my head. Just yesterday, I finished playing through Mega Man X8 for the first time, and I suspect that less than 20% of it involved what I would call Mega Man-like gameplay outside of the boss fights. I thought the idea of letting Axl earn new guns from bosses with no energy limit was neat, but there were so few moments in which I was walking forward, fighting enemies and jumping over pits, that I barely got a chance to play around with them.
None of these games are very long. Despite that, the designers took the time to program eight unique weapons for each game, and in later cases, for each character. That's a lot of gameplay content to mess with, and it's a big reason why Mega Man is so memorable. In my opinion, taking those away for even this long is the start of a long series of mistakes that eventually had me wondering why they bothered with anything more than jump and shoot if they're so unwilling to stick to the main gameplay style.