I wouldn't call myself a collector but the Jag has been my main focus for purchases for a while. I bought my Jag in the 90s at the tail end of it's commercial life and picked up a lot of stuff cheap at that time. After a few years away from the system I've been catching up with the home brew scene.
The Jaguar does cover a lot of retro gaming bases: early FPS (Wolfenstein, Doom, AVP), platformers (Rayman, Zool 2, Flashback, Bubsy), shooters (Raiden, Protector, Defender 2000), 2D racing (Super Burnout, Powerdrive Rally), strategy (Syndicate, Theme Park), puzzle (Attack of the Mutant Penguins, Flip Out, Zoop), 2D Fighting (Ultra Vortek, Primal Rage, Kasumi Ninja), sports (Sensible Soccer, NBA Jam TE, Brutal Sports Football).
I also like a lot of the Jag exclusive titles like Iron Solider 1 and 2, I War, T2K, Battlemorph, Skyhammer (plus several of those listed above).
Having said that not all the games have aged well.
The Jag was my only console, apart from Lynx and 2600, until about 2002 but, as much as I love it, I couldn't get by with just the Jaguar. The call of survival horror games lured me to the PS1 (Silent Hill, Resident Evil etc), then Dreamcast (Resident Evil: Code Veronica, Carrier), then PS2, then X360.
Ultimately many of the Jags best titles are available on other, more mainstream retro systems for a lot less money which makes it difficult to justify recommending it to a new starter.
Where the Jag excels is the home brew scene. Rebooteroids is up there with the best games on the system and the ST / Amiga ports from AA, Piko, Songbird etc are all worth checking out if you have deep pockets.
Long live Jaguar home brew!