Two good games are better than one good game
But Castlevania Double Pack contains two games that are so similar that you'd have to be crazy to purchase them separately, at least now that you can get them together for a lot less. The package contains Castlevania: Harmony of Dissonance and Castlevania: Aria of Sorrow, and both offer traditional Castlevania-style dungeon-exploring monster-destroying fun.
The biggest problem with these two games is, thankfully, the one that the bundled status solves. The two games included are so similar that if you didn't have separate title screens and different androgynous whip-wielding characters, you might think it's the exact same game. Shelling out thirty bucks for each of these games when they were first released would have been a waste, because in many ways if you've played one you've also played the other.
But now the two are together, in one package, and at a budget price (if you can still find it new, that is). It's nothing particularly extraordinary, but Castlevania fans know what to expect: a lot of unguided, free-roaming exploration of a massive castle with hordes of enemies around every corner. It's not groundbreaking for the series and it's not going to convert any Castlevania-haters, but for fans of the franchise it's a worthy purchase.
Combat is largely a joke in Castlevania, and enemies can be defeated by whacking them a few times with whatever massive armament you currently have equipped. The real meat of these titles lies in the exploration. Much like games such as Metroid, you'll do a heck of a lot of backtracking as you search out new abilities that grant you access to previously-inaccessible places. And Dracula's Castle is absolutely huge, so exploration is quite a lengthy task.
At the same time, though, the sheer scope of your undertaking can be a bit overwhelming, particularly for novice players. After finding a specific skill, you may have to backtrack to the very beginning to access some little spot you never even saw the first time around. And when you've got eight or ten blocked-off areas at a time, trying to figure out where to use a new skill can be quite frustrating.
And that's pretty much it; there's not a whole lot more to discuss with Castlevania. It's very basic and if you don't enjoy the core concept of the game you're not going to like Castlevania. In some ways it feels like a chore: running around the castle trying to find out where to go next with a few engaging boss fights, barely any puzzles, and armies of easy-to-kill foes.
Admittedly, there are a few little twists to this formula that each of the two games adds to the mix, but they feel more like excuses to release a new game than actual gameplay mechanics. Harmony of Dissonance essentially has two "layers" of castle on top of each other, requiring you to switch back and forth to progress. It's an overdone mechanic in adventure games and only serves to double the size of your exploring grounds.
Aria of Sorrow does away with the "light-world-dark-world" idea and instead adds a little more to the mild role-playing elements of the series (defeating foes gives you experience and you can level up along with equipping tons of armor and weapons). When you defeat an enemy, you may randomly receive its soul; these souls are used for a variety of purposes, from solving some really lame puzzles to defeating enemies in battle.
Of the two games, I'd have to say that however similar they are, Harmony of Dissonance is a bit better. I like the back-and-forth aspect, plus there's the fact that Aria's soul-collecting mechanic never really works like it should. Most souls that you collect from enemies work as secondary attacks, but 95% of the time you'll never use them because your weapon is stronger anyway. There are some souls needed to progress through the game, but you'll find these in the castle rather than defeat an enemy to get them, essentially negating the idea behind "kill a bunch of this enemy until you get its soul".
Castlevania Double Pack isn't a great game, but the fact that it offers two solid 2D adventure titles is certainly a plus. There are no huge differences between the two titles included, but they work well together because of it. The series' recent DS offerings are a bit better, but for twenty bucks Double Pack is a bargain. If you're into Castlevania and never picked up the package's two constituents when they first released, then the Double Pack is probably worth buying.