Crisis force.
Crisis force.
You beat me to it. I managed to pick this game up for the Famicom four or five years ago, and I've played through it with a friend at least once a year since then. It isn't anywhere near as challenging as Life Force, but that's why people agree to play it with me--you can actually beat the game without cheating. I know there are people who can beat Life Force without cheating, but I'm not one of them. Crisis Force is more of a casual shooter, and it's actually more enjoyable with two players. It's #1 on my list of Famicom games that should have been released in the USA.
Going to have to throw in my vote for the rather overlooked, (imo)
Monster in My Pocket.
I played it for years growing up without even realizing it was based on a toy/franchise. Anyway, good fun with coop, and a decent challenge too. It's a beatemup/platformer. The music definitely has the Konami feel, too and there's some memorable tunes in it. Give it a shot.
Monster In My Pocket is decent fun if a bit bland (the same for the toys, really). It's a short ride, but at least the final boss is a bit tricky. One thing I find slightly annoying is that since the game is presented as a platformer with most enemies coming from the direction you're moving in, it's easy for one player to run ahead of the other and soak up the majority of the action while the other player runs along behind doing nothing.