I usually have only bad things to say about Vanillite and its evolutionary relatives, but today I realized I might reconsider that opinion:
Vanillite, Vanillish and Vanilluxe represents one of the only instances of Game Freak actually trying with Ice-type Pokémon. Trying and falling short, for the most part, but the core idea is miles better than what Ice usually gets. Let me write an essay list the reasons why:
First of all, some trivia: Can you list all the three-stage evolutionary families that begin and/or end with a Pokémon that is at least part Ice-type? For most Pokémon types, that would be a daunting task, but for Ice, it's easy: Swinub line, Spheal line, Vanillite line, that's it. As far as I'm able to tell, Ice is the typing with the fewest three-stage lines. All the others have at least five lines which fit the criterium above. Even Fairy, which was introduced last generation, has six full three-stage lines where all three members have the typing, plus one where only one member is Fairy (Primarina's line). Ice has been around since Gen I, but its Pokémon are mostly single- or two-stage. Vanillite and its family is a honest exception, and also among the first evolutionary lines to be pure Ice from start to finish (the first was Snorunt's line, although arguably Froslass messed that up).
Second, its availability: Surely, we've all noticed by now that Ice-types are almost always introduced late in the game. It is as if Game Freak is restricting Ice-types to ice/snow areas only, and those are always late. We did some digging around this on IRC a few months back, and concluded that the Ice-type is usually the last type of Pokémon a player will ever encounter - that or Dragon, which was originally designed to be a late-game type. Interestingly, there has been an Ice-type specialist in every Pokémon region up to and including Gen VI. Here is when they appear: Elite Four (RBY), 7th Gym (GSC), Elite Four (RSE), 7th Gym (DPPt), 7th Gym (BW), and 8th Gym (XY).
Our aforementioned IRC data dig found out that the earliest available Ice-type in any game is Cloyster in RBY. You can fish Shellder with the Super Rod, and evolve it with a Water Stone, before you take on the 4th Gym. Unless you jump through similar hoops (backtracking to find Lapras in Union Cave on a Friday in GSC), you'll have to wait until after the 6th Gym to find any Ice-types in Pokémon games...
...with the exception of Vanilite. This little fellow is presented to you, readily available, before you take on the fifth Gym in BW. You don't even have to look for it specifically, it's actually a little hard to avoid since a visit to Cold Storage is mandatory and Vanillite is the most common encounter there. Cold Storage remains one of the only locations in Pokémon where Ice-types are available outside a late-game snow/ice area.
Third, Vanilluxe's stat spread: It remains one of the few Ice-types whose offensive stats are higher than the defensive ones on both sides of the spectrum, and Special Attack is its highest stat. With that, Vanilluxe is not only an offensively-oriented Ice type, which is a rarity in itself, but an Ice type oriented towards Special offence. Its Speed isn't half-bad either. Vanilluxe isn't unique in this regard (Jynx does the same), but it belongs to a very small minority, in a typing dominated by stat spreads fitting for glaciers or icebergs: Slow and tough, with high Defense, low speed and mediocre offense.
Interestingly, Vanilluxe has great synergy with Ice's type chart as well: Practically no resistances on the defensive side, but hits a lot of things hard on the offensive side. Ice's most powerful and reliable moves, Ice Beam and Blizzard, are both on the Special side of the spectrum. Ice as a typing seems to have been built for Special sweepers, but no Ice-type Pokémon have the stats to take advantage of it. Vanilluxe doesn't do it perfectly, but it's among the closest we have. The designers managed to sneak Ice Body, decidedly a defensive ability, on it, but in Gen VII Vanilluxe gets Snow Warning, which is much better suited for an offensive build.
All in all, Ice types are plagued by poor design choices, but Vanillite and its relatives should be commended for managing to avoid them for the most part. It is not built to be defensive, a job the Ice-type can't do anyway, no matter how high stats, great Abilities and good boosting moves they keep receiving. The Vanillite family sticks to what the Ice-type should do, which is hitting hard with the fantastic spammability of Special Ice STAB. Vanillite was not a late-game Pokémon in its inception, it made it possible to actually catch and use an Ice Pokémon for a playthrough of Black and White (a trick that has not been repeated since, sadly).
They haven't avoided every pratfall, though: Vanilluxe's movepool is as barren as the Antarctic interior. Overwhelmingly Ice and Normal attacking moves, with only Flash Cannon and Signal Beam for coverage. Vanillite's early availability was offset by late evolution, with sky-high evolutionary levels compared to their BST.
And I still dislike their design. But I've come to appreciate what Vanillite, Vanillish and Vanilluxe actually do, since they do it so much better than the vast majority of their Ice-type brethren.