This game has some major issues with its difficulty. Regular seems to be veteran, Hardened seems to be "Supersoldier" and it's incomprehensible how hard Veteran is. The use of a "Health" bar doesn't make things any better either. It seems that Infinity Ward had no idea how to make the game difficult, so they slapped in a couple of missions where you must hopelessly defend an area until reinforcements come and by scarcely placing health pickups in these situations. These are clearly the most frustrating aspect of the game and will have you on the verge of deleting it from your console in both annoyance and disgust.
I must say however, that this was Infinity Ward's first game, and for a developer's first game, it really is better than you'd expect. There are elements of the game which have paved the way for some of the most spectacular shooters of all time. I commend Infinity Ward's effort on this but I'm sure it would be much appreciated if the difficulty was eased off a little.
Call of Duty: Classic is worth a purchase. It greatly exceeds the quality and experience of most games up for online purchase. I personally wouldn't consider it as an "Arcade" game but rather an "Old-School" shooter that was great for its time. Unfortunately the steep difficulty level ruins this great action experience. It's great to see where the series began.