I own both the M50 and the Grado 225e, and they are very, very different headphones. The M50 is nice to bring outside home, since it's very solid, foldable and well isolated, but as you described it doesn't have that much details. It responds Ok with mids, but it doesn't really have any soundstage. It's great to listen to electronic music, or as a monitor headphone, it's Ok with most styles, but if what you need is soundstage than forget the M50s (I listen mostly to electronic music so it's Ok for me
).
The Grado 225e (which I own, along with the M50) are also a very specific type of headphones, even more specific than the M50 in my opinion. They are very nice if you listen to quiet or punchy recordings with a lot of details in the high-mids and highs, but on other types of recordings it doesn't perform as well. It has a little bit of bass, just enough to have an impact, but apart from that it doesn't have nearly enough low-mid for me, which is a shame. In fact, the problem with these is not that they are not good, because they are of great quality. The problem is that there is pretty much no style of music that fits them : you can't use them for electronic music because, altough they have great highs and are very punchy, they lack bass; you can't use them for classical music, because they lack the all-around frequency response that is needed for classical music (the absence of low-mid is really a shame in regards to classical music); you can't use them for jazz because, again, they lack the warmth that's needed for this kind of use. The only type of music you can really listen to is rock, because rock needs a punchy sound with proheminent highs; the only problem, again, is that you won't hear the drum's impact that much, or the bass (the instrument).
The only type of music it really works really well with would be folk or accapella. So, altough I like it for its clear sound, good details and soundstage, the absence of warmth and bass makes it very hard to use for most styles of music. That's probably why you love it or hate it. Also, they work a lot better when used with a good amp (like any headphone), that's when you'll start to hear the bass a bit more (altough it never really comes alive; well, actually, the thing with the SR225's bass is that it's punchy, but it's not maintained; it'll hit you but run away as fast
).
Here's an example of music they work well with I think :
https://www.youtube.com/watch?v=itLxXeyM2aM
Like liquidzoo, I'd suggest you try the Grados if you can, just to see if you like them, because they're definitely great for details and soundstage, and also impact. I think that, in the Grado line, the SR325e may suit you best (they're a bit over your budget but I think they have a bit more warmth, but I could be wrong). Oh and also, Grados are made to use at home! They leak sound A LOT.
Hope it helps!
Edit : Oh and, before I forget : the earcups on the SR225 make a BIG difference. If you keep the original earcups, they'll sound more punchy, in your face, but will have less soundstage; if you put on large cups (available on Ebay for a small price), they'll give you a better soundstage but will sound more ''polite'' as some people say, more like Sennheisers, less in your face. And, finally, if you pick flat earpads, the SR225 will sound less detailed and that's it (I don't really like the flat pads, it breaks the purpose of the Grados in my opinion
).
Because the M50 are supposed to be bad?
Oh and, suggesting the HD600 for a 300$ budget is absurd, since they are around 450$/500$ in the least, plus you need to spend around 150$ to 300$ for an amp, so it'll cost him/her at least twice what he/she's looking for...
And also, you've ''heard'' that the Grados are bad? Have you tried them or what? Please, we don't need trolls like you around here.
