There are quite a few good mods already out for the game.  One is a campaign extender which adds a significant amount of missions to the vanilla campaign.  I also play around with the Los Angeles Flight II/III mod, which introduces the VLS and MADCAP Torpedo to the game.  That makes it a lot of fun, and not so much of a pita to go get TLAM's when a mission arises.
One tip, don't take too many Harpoons.  They are just a guarantee that at least one helo is going to come and drop a bunch of torpedoes on you.  They also have naval bombers in the game and they love to drop torpedoes too.  Playing the game on the high difficulty levels requires a lot of patience and thought.