I’ve had a DSL 100 since probably 2003. I think it’s from 98 or 99 (one of the bad years?). I did have to have an amp tech look at it back in probably 2004 to fix issues that I had with Lead 2 on the Red channel. He noticed some bad solder joints and fixed those. Maybe some burning too if memory serves me right. It’s been solid ever since with only tube changes and biasing required.
As far as the sound, it does the thing(s) that it does really well. It’s pretty versatile if the Marshall flavor is what you’re after. I find that it sort of has its own thing going versus the earlier Marshall models (it’s not an 800, for example). It can sound close to your favorite Marshalls, and it does its own thing well. Green channel sounds great, but it needs a boost to get to higher gain levels. I tend to like boosted Green crunch the best. Red channel is leaner sounding than Green and way higher gain. Also a great sound.
The amp works well with different speakers and cabs. I’ve also tried (probably) hundreds of IRs, and the amp isn’t as picky about speakers/cabs/mics as my Dual Rec, for example. It also likes boost pedals. My favorite with it is probably an OCD or just a clean boost, but it takes Tubescreamer style pedals well too.
Probably not the best choice for modern metal, but I’ve seen videos that prove me wrong on that assertion.