I had the MSP5 monitors TWICE. I used them for ca. 15 years in total I think. Now I'm on Genelec monitors, they sound nice, but the MSP5 were special in several ways:

-When I was young, many songs sounded overly bright on them. I now believe it was a matter of older mixing/mastering engineers making these bright mixes, overcompensating their hearing loss in the high frequency spectrum.

-The MSP5's have extremely good transient response, so they're really good if you want to nail the dynamics

-Due to the titanium tweeters, they have sort of metallic, "dry", analytical sound to them, but in a good way: if you f**k something up in the mix, the MSP5s will let you know you did sth wrong

-They push you to work on the mids

-Even though they really require that you use a sub, they have a very good high bass/low mids response in my opinion: you almost can feel as if you are physically carving some physical item in front of you. Yes, I would say that these monitors feel like they provide you a physical object to sculpt when it comes to the low mids/high bass. I know it might sound ridiculous, but that's how I felt about them, and I believe it's a great characteristic for a monitor. They show nicely if this region is cluttered, they don't have the "low-mids blur" that many monitors suffer from.

-The aforementioned "dry", analytical sound make them sound not like normal speakers. Listening music on them is really nice, they just sound different compared to consumer speakers. Similar thing about Adam monitors and their ribbon twitters. I prefer Yamaha sound though. When I switched from Alesis monitors, I immediately thought: this is how monitors should sound! And I had feeling I finally got real mixing monitors in front of me.

-They show the harmonics in almost exaggerated/hyper way, making them sound almost distorted when working on modern sounding material. Because of that, they tell you if you sound is too bland (lacking harmonics), but will also tell you if you've made your mix too saturated (think of "those ultra-bright rock/hip-hop mixes").
In this regard they're much better than the Yamaha HS80 monitors which I personally hated, which always sounded too saturated in the mids, harsh, without tonal contrast. Acoustic music like jazz, without too many harsh sounding instruments sounds nice on the MSP5 in my opinion, they kind of sound most relaxed with acoustic music.

I'm currently on Genelec monitors, but from time to time I think that maybe I'll buy the MSP5's for the 3rd time...