A long time ago, I was in a summer program that went on for a few weeks. I enjoyed it, and one of the years, I met a leader who enjoyed Metal Slug. Fortunately, that same year, i was in the group that got to go to an arcade. He and I played some co-op Metal Slug, and let me tell you, it was really fun. Once we were done, I asked him what his favorite and least favorite were, and he said that 3 was his favorite and 4 was his least favorite. I don't remember why, but I eventually met a different person on Discord who also loved Metal Slug and said the same games were her favorite and least favorite.
This is part of the reason why I touched on MS3 last year as well, was my friend telling me to talk about it. I didn't think it was a half-bad idea, and I enjoyed playing through it, aside from the final level dragging on forever.
So, with having had played Metal Slug 4, what are my opinions on it?
I thought it was alright, having had played through the whole thing. I'll say, not having a 30 minute level definitely was a positive, but while that level did drag on for a while, it made MS3 unique. MS4 on the flipside has nothing really to make it unique. It brings nothing really new to the table, just another ~45 minute Metal Slug game.
That, however seems to be everyone's problem with it. It is bland and ununique. Does that mean it's bad? Well, bring up the 3D Metal Slug game and they'll say that it isn't as bad as that is, but if you have to compare it to the actual worst game in the series, is it really that good in the first place?
Gameplay wise, Metal Slug 4 plays like Metal Slug 3, but in a similar vein to 5's direct port to PS2 and Xbox, it is strictly the game and nothing really else of note. Weirdly, the voice clips used for the weapons in this game are different, even though they went back to their original state in 5. There's 6 levels in total, and while they don't run as long as Metal Slug 3's levels, they tend to kind of blend together. That can be a good thing, but as far as I remember, Metal Slug 4 doesn't have any branching pathways like 3 did, the levels are all purely linear. Also, there's no Eri to be played as, only in transitional scenes and the end scene where all the playable characters get fat. Play through 6 levels chasing after the long-running villain and you eventually fight a final boss that is a pain in the ass and is a scientist. He's a pain, because most of his attacks are nearly unavoidable.
That beam in the center you have to jump over as well. It works really weird.
As a side note, Metal Slug 4 got a CERO 15 rating in Japan, and I don't really understand why, because even Metal Slug Complete/Anthology got a 12, and that contains MS4. It's bizarre, and the only difference I can find is that some of the bomb pickups turn your bombs into a Molotov cocktail, the local drink. Even if they are called "fire bombs", they are Molotov. I only make note of them is because of how they tend to be used in political violence, and how tutorials for making them can be found all over the internet.
Music wise, I don't really have any that are noteworthy, just all of them are merely OK. MS3 had some, especially the first stage theme, but here, it's not really of note. I already said that the announcers voice was changed, which isn't nearly as good as him shouting "ROCKIT LAWNCHAIR!" It's similar, but it's not the same anymore.
Graphically, it looks like Metal Slug, which is a good thing.
And the zombies from Metal Slug 3 make a return... yay...
It controls well as well, I never noticed any times I called BS because of input lag, it's good. It plays well with a fightstick too.
No bonuses such as storming the UFO, it's bare-bones as previously mentioned. It's unfortunate, because this game could have done with some extras, being that you're not likely to play it over and over again in one sitting. If there are any real big problems or bonuses with co-op that I didn't touch on because I didn't get to play it in co-op, then my bad. That's just the way it goes.
Overall, would I recommend this game, or even say that it's not that bad?
No and yes. It's not really noteworthy, but it's not a terrible game. Just because lists and fans may say it's the worst Metal Slug game doesn't inherently mean ti's bad... unless it's the 3D remake. If you want to play this and you want the PS2/Xbox port, then be my guest. I don't fully recommend it, but you can do that.
Also, the Japanese version doesn't compress well at all. That's frustrating, especially since the game is 3GB and compressing it shaves off 40MB. If that space could have been used for something... useful instead of just dummy data, that wouldn't be a big problem. But, that's just a nitpick.
Play it if you want, but it's not a must-play.