Cadash is one of those nostalgic favorites that aged poorly; it seemed much better back in 1989, when the alternatives for a side-scroller with RPG elements were mostly limited to Zelda 2 and the Wonderboy series. The original arcade release had the ability to chain two cabinets together for four-player action, making it something like the side-scrolling incarnation of Gauntlet. While it was pioneering in some respects and has qualities that still hold up twenty years later, it is also a frequently tedious cheap hit fest that offers the solo player very little compelling reason to stick with it.
As with most games designed with a multi-player focus, the more peeps you can get in on it the better. Unfortunately, the programming is restricted so that all four people have to be on the same screen at the same time (no one can scroll any farther in any direction than the screen limits of the middlemost character of the bunch), but with two to four people playing the game flows more the way it was intended to. A solo player has to be careful in character selection, as the Priest and Wizard characters were really not designed to be used unaccompanied, and they can quickly find themselves dying way too often and grinding it out in overlong boss battles where they can't do adequate damage.
The gameplay is basically decent and has held up over the years, but there's a little too much of that early Castlevania "approach you from awkward angles your weapon wasn't designed for" enemy design philosophy that always seems cheap and frustrating. Spell casting and item use are also a little awkward, as they are lumped together in one menu accessed by holding down the attack button and releasing when the appropriate spell or item pops up, and the cycle takes so long you'll inevitably find yourself getting pwned just before you can get a healing or armor spell off.
One last point of note is that Taito apparently wasn't yet experienced in translating games with a decent amount of text, so the localization is one of the more notoriously Engrishy ones of arcade history. Exclamations like "How well you came!" and "In flont is a hidden spring" are the norm here.
Cadash is overall a great concept, executed moderately well, but a little too basic and primitive to be an enduring classic. If you can get some buds together to play it, it can be fun for a romp however.
* Gameplay Video