Best offensive type, worst defensive type.
Ice has the best offensive profile of any type in the game — Ice moves are super-effective against Grass, Ground, Flying and Dragon, which is the entire top half of competitive metagames. But Ice's defensive profile is the worst in the game: only resists itself, and is weak to Fire, Fighting, Rock and Steel. You build Ice teams for hit-and-run, not for attrition.
Ice is the ultimate offensive check to Dragon-based metagames. Hail teams (Aurora Veil + Slush Rush sweepers) are one of the most degenerate strategies in competitive play, giving Ice mons defensive screens and double-speed on weather.
Ice Beam (90 BP, 10% freeze) is the gold standard. Icicle Crash gives physical Ice mons a flinch-chance option. Freeze-Dry is unique — it hits Water-types super-effectively, bypassing their Ice resist.
Articuno was the first Legendary most players ever encountered — hidden in the back of the Seafoam Islands in Red & Blue. It was also the weakest of the Kanto Legendary birds statistically, which is why Ice's reputation for fragility stuck.