As a systems platform it remained top notch until the very end. That is the JA37 fighterversion. The latest D version were in fact superiour in some respects to the first batch of the JAS39. I think it was a pioneer in the datalink department, including fighter to fighter, already in the 80´s. For example the (radar)passive part of a two ship formation firing the missile while the other illuminating. Or covering a large area with few planes and great spread since they could share their display information in realtime.
Other special characteristics were the extrem longshooting and accurate 30mm Oerlikon (Swizz or Austrian made) cannon. IIRC it was first developed as an antiaircraft gun. They also used to boast about its climbrate - from standing still 0km/h up to 10000m in less than 90 seconds. Haven´t got a clue how that compares to the rest really...
It´s pretty clear it wouldn´t outturn any of those Pilatasso mention, but probably would give them a match in a slow speed fight. It is known for being a very responsive "pilots aircraft".
I managed to see it in two airshows last summer, and it just outclasses the JAS39 Gripen as a display act. Yes, Andrew_McP put it very well... it does look brutal on the ground, but in the air the impression is quite different. Actually, the most impressive is just seeing a two ship take off for a mission without any show :).
Patricksaviation.com delivers again. The fighterversion (and at least some surveillance version as well) have a taller fin which is protruding a bit backwards, compared the attackversions, which just go straight up.
http://www1.patricksaviation.com/uploads/videos62/Viggen.mpeg