If it is well-maintained, don't hesitate to get it.
I've had a 1998 Acura SLX for five years now - excellent vehicle overall. It is Acura badged but underneath it is the larger Isuzu Trooper. The Trooper and Rodeo share a tremendous amount of parts/design/engineering, and I've learned a lot about both and can share some points. The place for good info is planetisuzoo.com. All technical issues can get assistance there.
Overall quality/reliability: On mine, it's on par with our 10 year old Lexus and several other Toyotas I've had; much better than any German or US car I've owned or am familiar with. BUT: The Trooper/SLX are Japanese assembled, the Rodeo in Indiana. This may lead to some differences in overall quality as it does with the Land Cruiser/Sequoia pair where one is Japanese made and the other in, coincidentally, Indiana.
Engine: There was a 4 and 6. The 4 I am not intimately familiar with but think it's a non-issue. The Six had issues with oil control ring coking as did the 3.5 from 98 to very late 2001. This leads to oil consumption. The reason was inadequate drain-back holes in ring grooves and on skirts. Same as Saturns and Toyota 2.4s from 1995 to ~2005. How did so many engineers make the same mistake? It can be controlled with a piston soak, engine cleaning, and high quality synthetic HDEO or HM oil (I have done it, it works). The V6 is otherwise a very durable, reliable engine.
If it is a very late 2001 V6 with a screwed-in PCV valve, it could have the updated pistons/rings and be free of this issue. As would any 2002 or later.
Transmission: No issues I know of for the I4 manual. The V6 was mated to a GM 4L30E. It can be described as "adequate" - it represents the high point of GM design and French quality (they were made in Strasbourg, France). The real issue is that they are "sealed" with the drain/fill hole underneath, no dipstick. As such, no one ever services them and if they leak and get low, can ruin friction discs or other parts. If the transmission is good and has been serviced, you are fine. Just keep it up. I'm retrofitting a dipstick to mine this summer. Problems are more common in the heavier Troopers which saw more off-road abuse.
4WD system: Very robust, with a Dana rear and Borg Warner 44 series t-case. Electronic push button. For less front end wear and increased MPGs, you can remove the front "auto" (fixed) hubs and retro-fit older manual switching Aisin units. CV boots last forever now, and improved MPG and lighter steering.
Parts: Widely available at any store for most, plenty of body parts from yards. No issue whatsoever and as cheap as anything out there.
Overall: I have learned to really appreciate Toyotas, but I bought this SLX vs. a comparable era 4Runner and am really glad I did. I want to replace it with something larger (V8 Land Cruiser), but it's simply too nice to part with so I'll keep it until my step-son can drive and let him have it.
You could also consider a late model Trooper/SLX which give a lot of performance for the $, with better power and room, and Japanese assembly with excellent quality. Just watch the oil and service the transmission.