Haven't we met somewhere before?
Oh yes, now I remember. Last time I saw this game, it was called “Joust.” An undeniable classic, Joust serves as a blueprint for Mario Bros. (MB) to follow. Don't get me wrong—that's actually a good thing!
MB borrows the 2D, one-screen, two-player simultaneous action of Joust, but the eponymous brothers do not ride giant birds into battle. Instead, plumbers Mario and Luigi run and jump all over the sewer in what I guess you would now have to call the standard, Super Mario-esque platforming style. The graphics and sound are certainly not of Super Mario quality, but here the NES port is merely reproducing faithfully the original arcade game.
The list of minor variations on the original theme goes on: Joust's shrieking pterodactyls are replaced by balls of fire (or whatever the heck they are supposed to be) that sweep across one level of the screen at a time; the grabbing troll hands from the fiery depths below are replaced with the "freezing" enemies from above; and so forth. It's a pretty well-balanced design, reasonably challenging but not overly frustrating.
As I've already said, Joust is one of my all-time favorites, and so the fact that MB was obviously, shall we say, "inspired" by that earlier hit is a plus, not a minus, in my book.
No, the main problem with MB is that it seems shallow and limited compared to its vaunted descendant, Super Mario Bros. (SMB). And consciously or unconsciously, you can't help but compare. The fact is that most people have played SMB and its sequels, and so they will come to MB later on expecting something similar. However, it is almost inevitable that MB will disappoint. SMB totally broke the mold and shattered expectations about video games. MB was from that old mold, as becomes all too apparent as you play it. SMB plays fast with tight control; by comparison, the Mario and Luigi of MB seem slow to move and respond to your commands. You can adapt to it, but it just somehow never feels quite right.
Really, the only thing MB has that SMB doesn't is the simultaneous two-player option. Many people like myself are almost exclusively solo gamers, though, which relegates MB to more of a collector's item than a game we'll actually play very often.
The Bottom Line
I would call Mario Bros. a "semi-classic." It's worth playing just for its historical importance as the missing link between Donkey Kong and Super Mario Bros. But unless this happens to have been the favorite game of your youth, I doubt you’ll play it very much.