Wow, so many responses so quickly! Thanks fellas, I really appreciate the effort.

Based on my poor description, it does sound like a Metal Slug game... but it wasn't animated as well and the character sprites were larger. The character sprites were about the size of characters in Thunder Fox, seen here:

They had about the same quality of animation as in Thunder Fox too--not terrible, but not incredible. I'm quite certain this wasn't a NeoGeo game at all. I should have said that up-front. My apologies.
Unfortunately, it wasn't Contra or Battle Rangers either, although those match my bad description as well. You guys are sharp. The graphics were a bit more detailed, such as in Thunder Fox (above).
I would say the closest match so far is Ikari III:

However, this was a side scroller with some depth to the playfield. Much like, say, X-Men when the screen scrolls left to right.
I was thinking about it and I also remember in the attract mode play, after the players advance to the shoreline, they inflict some type of large explosion on the enemy which nearly fills the screen for an instant with red and yellow. Shortly after that the attract mode cycles back to the title screen or highscore table. I know... that probably doesn't help much.

Thank you all again for taking the time to reply.
