Its too long to explain. Im sending you a private message.

You won't regret it.

The game has a demo available, although IMHO it doesn't do it justice.
The demo consist of a small independent 'adventure' that has nothing to do with the full game campaign, has a fixed party (you can create your characters in the full game), and I feel it's not well balanced at some points.
Still, it gives you a general idea of the gameplay, it may be worth to try it if you're unsure.

I'd love to play Knights of the Chalice, too, if only it would be a little cheaper ...

If you don't want to spend as much money, Telepath RPG is a turn-based strategy-heavy game. No idea if it's good though, you might want to check some reviews. Usually it's pretty expensive, too, but it's currently featured in the IndiefortBundle, which means you could grab it for a few bucks, along with two other games of your choice (provided you don't mind downloading them via GamersGate).

As for the GOG's, did you check Realms of Arkania and Betrayal at Krondor? The Goldbox games might be good choices, too, unless they're too old-school for you, but unfortunately I have no idea where to buy them at the moment.

If you don't mind older games, Ultima 6 and the two side-games based on its engine (Savage Empire and Martian Dreams) are tile-based, turn-based, and involve a party.

The latter two are freebies and the former is part of one of the Ultima collections.

(The earlier games of the series are also tile/turn and (sometimes) party-based, but they're also MUCH older technologically and that may make them less approachable.)

Played Fallout 2 with Unarmed and the Super Sledge. It's really fun.