Torchlight is ARPG in the same vein as Diablo, not really CRPG.

BG1 is a good game, BG2 being better. Just be sure to read a manual, it is based on AD&D 2e and requires some knowledge of its mechanics.

If not BG1, is there another CRPG you recommend I play as a new comer to the genre?

Depends of what you're expecting out of it, but I'll assume that you're thinking of isometric CRPGs in the vein of Interplay's golden RPG era (like BG1/2).

If you want to play what are considered the best, at least among core CRPG audience, then it's Fallout 1/2, Planescape:Torment and Arcanum: Of Steamworks and Magick Obscura, along with BG2 - keep in mind though, they are all quite old and come from the time when Interplay and folks around it revitalized the genre, late 90s/early 00s, so from modern perspective they can be rough around the edges, though they do remain the best in the genre. Planescape: Torment is considered to be best written CRPG of all times, but just like BG1/2, it's also AD&D 2e based, so requires some basic knowledge of it (after you play one of them, you'll be set for the others, along with Icewind Dale 1/2 as well).

If you want something more modern along those lines, Pathfinder (both Kingmaker and Wrath of the Righteous), Pillars of Eternity 1/2, Wasteland 2/3, modern Shadowrun games (Returns, Dragonfall, Hong Kong), Torment: Tides of Numenera, Tyranny, Divinity: Original Sin 1/2 and, of course, Disco Elysium (being most unique of them all).

If you want something from this modern CRPG renaissance (that started with Obsidian's Pillars of Eternity Kickstarter back in 2012) that is probably most innovative, but quite rough around the edges due to much lower budgets, and not very mainstream friendly, then it's Kenshi along with Age of Decadence.

For some more indie stuff, check out UnderRail and Space Wreck.

Of course, this is just a subset of what CRPGs are and recommendations for just this particular type of CRPGs, being brought into mainstream spotlight via BG3.

EDIT: Almost forgot - if you want to see what D&D 5e is about, at least mechanically, Solasta: Crown of the Magister is game to play. It is not that of great game overall (with some user campaigns being actually better), but when it comes to recreating tactical combat of 5e, it's as close as you'll get apart from playing at actual table (since it tries, and manages, to be very true to tabletop 5e rules, unlike BG3).

EDIT 2: Hm, not sure what's up with my brain today to forget to recommend you Dragon Age: Origins. While not one of my favourites, it is quite good game, with actually well written companions, if that's what you're after.