Mario Adventure is a pet favorite of mine. It's the only hack I come back to over and over, enough that it's a distinctive favorite of mine as opposed to the blur of SMW hacks. What makes it stand out is the carefully from-scratch crafted visuals and design, and some creative twists on the Mario formula.
If I were to offer a comparison, it would be the transition of Ocarina Of Time to Majora's Mask; going from Super Mario Bros 3
to Mario Adventure is very like that. It looks and feels the same, but while the former codifies many of the franchise's unique elements, the latter creates some new concepts and ideas while playing with old ones. Perhaps the biggest draw of the game is, fittingly, the more adventurous feel to it; you can play the first seven worlds in any order you wish, meanwhile you'll be searching for their keys and collecting cash to spend on Toad Houses. The level design is quite professional and can be difficult; however, it rarely feels cheap or frustrating, and the weather effects keep things from getting stale and monotonous. Koopalings and drones both have gotten upgraded, more threatening than ever before. The final battle is also quite engaging.
However, there are still some questionable design elements. While the Fire Flower makes Mario into a superhero, it means the unchanged Super Leaf will almost never see use, creating a rather imbalanced array of power-ups compared to Super Mario Bros. 3. A few other design elements are also notably inhibitory: you can't leave a world without resetting or beating the Airship, some levels have a special mission that isn't clear (collect X amount of coins, usually), and the Boom Boom battles begin to just feel like a time waster rather than an actual challenge. And while this is more of a personal preference, Colossal Classics didn't seem to pan out quite like it could have, as the giant landscape often means the level it's actually redesigning will fly over your head. Some of the key hints are quite unintuitive
as well, and replays will lose some of their charm when you know the locations of all the keys. Finally, instead of item shops, you pay for the chance to gather items, which can just lead to frustration and lost coins.
Despite complaints, this hack is a must play for Mario lovers. It's just the right combination of new and old.