Re: What's the General Consensus on the first six SM games?
Super Mario Bros.: Controls very well in an era with lame platformers like Ice Climbers and Mario Bros. It's not that great today, a lot of newer games improve on the platforming (being able to bounce off enemies with the jump button, world maps, screen being able to scroll back, wall jumping, Mario not shrinking to small when hit as Fire Mario) and enemy item and level variety, and there's even Super Mario Bros. DX for Game Boy that improves on it.
Super Mario Bros. 2: Stands out from the rest, my favorite of the first three. I don't know what to say, there hasn't been games that improved on its gameplay since there are practically no successors to it, and it's worth a shot, especially if you want to play the notorious Advance version with all the hilarious yelling.
Lost Levels: Good one. Not the game though.
Super Mario Bros. 3.: Actually fun and far better than Super Mario Bros., feels closest to a New Super Mario Bros. game, but IMO, it's still feeling lacking. The levels feel way too short on average, no wall jumping, mashing button to fly is very lame, forcing players levels back after being defeated is extremely annoying, "Luigi" still has no point in this one. Despite it being the best of the Mario games on NES, it still doesn't hold up compared to New Super Mario Bros..
Super Mario World: Probably the best of the classics and still worth playing today because its concepts haven't been done to death, such as cohesive world, crisp and bright sprites (wellll Mario is ugly as sin), Yoshi is fun to use. The easiest of the classics by far though, and it's easily busted with the Cape and Blue Yoshi, and powerups are really generous in the game. Also introduced Star Coins and alternate exits, which gives players incentive to not just rush through the level (looking at you, Super Mario Bros. 3), giving the game a bit of replay value.
I generally prefer the New Super Mario Bros. games over these.
pedantic words tip: "general" isn't necessary, redundant with "consensus"