Well every game should look like or better than galaxy now or Brawl.
Mario Kart Wii- Too much like a desaturated Double Dash (but fun nonetheless.) I think MKWii could've easily looked like Galaxy, at least.
Strikers series- Awesome, actually a concept of time because there are actual shadows and some places are set in the evening, basically. I really, really, hate generic round or dodecagonal shadows under EVERYTHING besides Mario. Also, Mario has a more serious kind of attitude, always looking likes he ****ed/he's a lot cockier, which is cool. (Use that in the next Mario)
I've always envisioned a Mario side scroller that goes like kill-a-guy extreme old-school bringing back everything from the old ones but looking like Brawl (Mushroomy Kingdom, folks) minus the wasteland look. I'd save it for a SMB3 World 2 type thing. Basically, take NSMB, Wii it up, make it cooler, take out those weird, new shell enemy thingies in world 5, and make it about 75 times harder and longer.
Grass is actually blowing in the wind, question blocks glow and illuminate things around them, especially in an evening or night level. In the night it'll be clear enough to see galaxies from SMG or see star bits. You might see Rosalina and the observatory rocket by (don't give me the "she only comes once in 100 years" crap because she's apparently chillin' at Mario's house or the observatory since she's in Mario Kart). Give a sense of time going by!! The smiling clouds in the background should look real and start transforming into cumulonimbus clouds thus turning into an angry face and have a storm happening in the distance (Thank God for SMRPG and MK:SC for bringing them rain for once); have a rainy level for once! The storm could come by and drench you, graze you, completely miss you, etc. When you hit blocks they blow a bit of dust out and crumble to the ground rather than turning into 4 little blocks and falling into the "boyfriend box" (heard from a post long ago). You should see houses, tracks from Mario Kart in the distance, old levels set up in the background, questions blocks and music note blocks floating about in the background (just like the SMW cartoon). Whatever object you're going to encounter on the mini-map (toad house, etc.) should show up in the background when you get to towards the end of the level that precedes it. For example, NSMB- when you go to a warp cannon, the world shown has the corresponding level background for it, which is enjoyable.
Music- All the oldies and some new ones but orchestrated with a beautiful concert feel, i've always like violin parts in mario stuff. do it again!
Tons more ideas, but I've typed too much and forgot some, but you catch my drift.