Back in the day, many people tried remaking other Mario games with SMW's engine. This one tries to remain looking like its base ROM, Super Mario World.
For the most part, the level design is accurate to the original. There are a few missed spots: I noticed one missing hidden 1up that was not where it should have been in one level, and two stars side-by-side in another level when no such thing occurred in SMB.
This remake still has the bonus game from SMW and uses the goal tape instead of the flag and the fireworks, respectively. It also tries to compensate for what back then was a lack of custom sprites by adding in similar-acting SMW alternatives, such as with the slow-moving mushroom scale platforms which don't break after a certain balance like the SMB counterparts do.
Difficulty takes a major hit compared to the original and SMAS incarnations for three major reasons: physics, item carrying, and no restriction on scrolling the screen to the left. Most players won't notice any increase in difficulty until world 5 or 6 as a result. The smoother physics of SMW's player makes it easier to maneuver around tricky spots and over infamous gaps. Item carrying completely breaks the challenge most of the Hammer Brothers would give you, and those were absolute hell to face in SMB in 8-3. The freedom of scrolling also means those castles you have to try to find the right path lose their gimmick - some have a dead end and make you go back but you can see the right way, and others don't even try to stop you.
There are some level-specific things that ruin difficulty too. The star lasts a few seconds longer than it should. While there's no universal impact, it does defeat the challenge in those levels that have the star. Having a reserve item marginally makes the game easier than it already is, but often times, you won't even be needing it. Bosses also never throw hammers so those later castles don't present much of a challenge, except Bowser due to the structure above his bridge but he still has nothing on his original setup.
On the other hand, warp zones are null and will just lead you back to the start of the level. In SMB1 and SMB2 (Lost Levels) you would be taken to another world. However, even if the warps did work as it did in the original, it's null for this reason: the overworld is wide-open so you can play in any order.
What pissed me off was the ending because I got stuck inside the level and forced to die. It felt like a slap in the face.
If you want an easier SMB, this is for you. If not, look elsewhere.