I'm not that picky about maps (I've been slowly but surely working through the beatmap packs starting at the first), but I can give you a few guesses as to what people might find off about that one (and older maps in general):

• It's CS3, AR8, yet five stars, which is already breaking the modern convention. It might feel like a very unwieldy hard or normal diff to someone used to CS4AR9.
• An early part is full of straight sliders and movement at right angles. It's distinctive, but could come across as a boring gimmick these days.
• More frequent use of distance snapped jumps, and jumps at "plainer" angles - there's more variation in jump length (often longer/faster) and angles (often triangular) these days, which this map lacks relatively speaking. If you're used to these sorts of variations being used by the mapper to represent the music, older maps can end up feeling full of missed opportunities.
• Mapping to vocals - this is another thing that generally becomes more common the older you go in maps. I feel like it's gradually lost out in favor of instrumentals, which are generally steadier and more predictable. The way vocals can improvise on timing can be very beautiful, but it has a cost in how frequently a player's intuition will be off. In a way, predictability plays into readability (and even subjective "flow") on newer maps. The downside is that maps can start to seem interchangeable if this is too heavily emphasized by too many mappers.
• Missing piano parts and guitar solos in favor of a mapping to a steady drum line - I'm almost certain that a newer map would side with these fairly dynamic parts of the music, rather than keeping to a more steady beat there. As the years have gone by, from the original games that inspired osu! to today, there's definitely been significant changes in mapping philosophy - what parts should be mapped, and how they should be mapped, etc.
• Stream stacks - several "streams" in this map are just a stack of fast notes. These have definitely become less popular - it'll seem less readable compared to what are considered "normal" streams these days, and there's a potential sort of awkwardness to having fast keypresses combined with slow cursor movement.
• Little stream timing outside of the above - many newer maps often use triples or short streams (sometimes used as lead ins/outs for sliders) as their way of representing the music (even if they're not strongly indicated in it sometimes). The sort of dynamic these create can be pleasant, but this map was pretty clearly created before that sort of convention become popular.
• Song length - on a different note, this map is over five minutes long. As fun as marathons and long maps can be, trying one out in multiplayer (especially if it's with randoms, or on a song that people will be unfamiliar with) can be risky, as any dislike someone might have for the map/song tends to accumulate (regardless of how much you might love it). Sometimes the reverse can happen (ex. comments on this map] with long maps, but it's not something to count on.