Apparently someone timed out on my Marioary stage, not in the underground or near the goal but in the very first screen. And someone skipped my Mushroom World 1-1, I don't even...
Some people are really pushing it, feels bad man.
Anyway I played some of the GAF 1-1 levels. Here are my first impressions:
Super Mario Adventure: World 1-1
I like the setting, basic mechanics and enemies. Plus for the mushrooms and toad house. Some minor dislikes are the aesthetics. The pipes used for decoration look a bit weird, in particular the part where a few join eachother. I also don't like it that question blocks are under mushrooms, could be personal taste. I guess you ran out of space. Also don't be afraid to use coins to lure players, I've seen a lot of arrow use, which is not bad, but I think the direction should be self explanatory.
My major issue is, it does not start as a 1-1 level. The player starts really really high in the stage and that in itself can be pretty scary. It is on itself a fantastic stage and I'm really nitpicking here. Definitely replay it for the secret.
Adventure 1-1 ~ Grass Outskirts
Looks fantastic, good use of coins, fun little bonuses. Blocks lining up with the semi solid blocks makes it look weird after destruction. The vine in the block is too suspicious, add a block or two next to it. Feels like there are a bit to much enemies that can harm players. Love the usage of blocks for pipes with an angle.
It looks really neat all in all, but maybe a bit too hard for newcomers. Also on my need to replay it list.
Basic introductions
This one is a bit too simple perhaps and suffers from weird placement in the first screen. Two mushrooms and two goombas and if I miss it takes way to long to bounce off the pipe. The goomba will catch up. The blocks are 2 tiles high, making it a bit too narrow.
I feel like the pitfalls in the middle are not neccesary, maybe you were trying to teach player to triple jump? No warppipes killed me.
Could definitely do better with some secrets and better placement. It feels a bit unfinished, however I think you have the right mindset in it's simplicity. Just work from there to improve it
Underground Tutorials
I like the idea of the underground tutorials. It's safe enough to encourage players to play with it, but it does not necessary mean players will pick up on wall jumping. Especially if you're really stingy with power ups. Then in the overworld you remove the safety net, which is some a cool Nintendo-ish concept, but it's not excuted that well. I even died on the first wall jump lol. The P-switch is a nerve wrecking device and I failed to execute it propely in the overworld. Got a shitty goal ending, because the P-switches don't respawn. It feels like you're punishing players a bit to much. I think it's awesome you're tackling some more advanced techniques, however it's not yet a 1-1 level and thus the concept backfires.
1-1: Super Mario GAFWorld
A bit heavy on the enemy count early in the beginning. The flipable blocks look a bit lonely in the first screen. It is a lot of fun getting the cape, yoshi and a fire flower. I like the consistency in the the block placement, however I would use one tile set for each of them. The secrets are fun, but may be a bit inaccessible for the beginner. I would also remove the autorun in your sublevel, it does not flow well if you enter from the other side.
It reminds me a lot of SMW, so I think it's a job well done. I think it could work with some adjustments, but I'm not really keen to replay this stage.
I'll be playing more tomorrow. I hope the feedback is helpful, enjoyed playing these little stages. Super Mario Adventure: World 1-1 is probably my favorite among them. The fact that I have some minor issues with it only speaks volumes for how good it is. Also Adventure 1-1 ~ Grass Outskirts looks stunning, achieving Nintendo-esque aesthetics. Just don't let enemies ruin it

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Played Neo Super Mario Bros. W1-1 as well, but it's not in this group. I have some minor issues with it, but I want to replay it soon. I think it would look better if you used blocks for the angled warp pipes and add 1 more bonus in the level.