Ys I and II first came out for the MSX in 1987 and 1988 respectively, but the version that really catapulted the series to popularity was the CD-based remake for the Turbografx-CD released in 1991. That remake was in a weird place - on the cutting edge of technology in literally being one of the first CD-ROM games ever, but porting over gameplay from a early restrictive form of the MSX. The result was the stiff "bump combat" of a primitive PC game paired with one of the first Redbook Audio soundtracks and uses of voice acting and animated video.
The "bump system" was probably primarily a result of limitations in hardware and programming knowledge, but it also did serve the function of streamlining the typical late-80s RPG experience. Instead of slowly loading into and out of separate battle screens, it was all handled contiguously as part of the normal gameplay - if the enemy was too far in level above you, bumping into them simply hammered or outright killed you, while if you were suitably matched to them, you simply bumped them to dispatch them fairly quickly. Same mechanics as using the "fight" command in battle over and over, except much less time-consuming, but also adding the layer of complexity of trying to out-manuever the enemy and hit them in the side or the back while not leaving your own flank exposed.
I mention all this because hardcore Ys fans seem to still love the "bump" system, and feel that the original two games just aren't the same without it. Hardcore Ys fans aren't exactly a huge market, though, so it's kind of surprising to see a release that holds faithfully to that system (remaking the game in more of a Zelda style was done with the DS port instead.) This version does make at least a few small concessions to modernity, however, and it turns out those little tweaks actually make a lot of difference in playability.
The biggest difference is simply allowing the player to move freely in eight directions and increasing both the movement speed and the overall size of game maps. This is the first iteration of the game that isn't locked in clumsy tile-based four-directional movement. It makes things markedly less difficult; in fact, it's almost too easy as the new "diagonal rush" destroys nearly all enemies with ease so long as they don't have any friends around to backstab you while you're in the middle of it.
More of the challenge of the first two Ys games comes not from the everyday action of fighting common monsters, but from a combination of very challenging boss battles and a somewhat mazelike structure that mandates a lot of exploration, backtracking, and solving basic adventure-game-style puzzles without any in-game hints or a map system. I suspect this is an even bigger barrier to enjoyment / bone of contention to newcomers than the "bump system"; I notice most of the really negative reviews that are already out there focus heavily on the obtuse goals and lack of auto-map as the points that really turned them off. I'm of a divided mind on the subject. There's merit to these criticisms, first of all - a portable game, designed primarily to be played during commutes and generally while out of the house, really shouldn't be asking you to hand-draw maps as you go. And if you're going to remake a game and sell it at retail prices to a modern audience, it's fair to gauge modern expectations and standards and make reasonable concessions to them. Ultimately however, as you probably have inferred from the 4/5 score, I find in favor of the game's design decisions here. For one thing, I played the entirety of both games through, and while I occasionally got a little frustrated by the game's lack of communication about what I was supposed to be doing next, I never really felt like it was being unfair about it. The mazelike structure and backtracking of places like the Palace of Solomon also was on the annoying side sometimes, but I found it was still not nearly complex enough to actually require drawing out a map to navigate. An auto-map would have been NICE, for certain, and I wish they had included one, but not including one really didn't degrade the game experience significantly beyond making it a bit more inconvenient and annoying at times.
So what's the purpose of hewing so faithfully to "outdated" mechanics? I feel that the uncompromising style of Ys Chronicles gives it an intriguing flavor that's absent from just about all modern gaming, a sense of mystery and danger that takes you back to the late 80s when the idead of action-adventure gaming was still a new and fresh thing. Further, this flavor is perfectly accentuated by the upgrades in art, music and gameplay. As such it's a bit of a connosieur's (you could also probably use the term "game snob") game, but the quality and care taken in what to upgrade and tweak and what to leave alone is undeniable and merits a high score. Oh, and the revamped soundtrack is killer.
* Gameplay Video