In my opinion, it is. It's a really awesome game. I hope that Capcom decides to add the other games to it, though... I'd pay for them.
No. It includes all 4 cases of the original GBA version as well as the 5th case added to the Wii and DS ports. Each case takes about 4-5 hours to complete (without walkthroughs), all in all there's about 25 hours worth of gameplay. If you like adventure games and mysteries, it's a no brainer.