The cool thing about the ability is that the land in question doesn't have to be a basic Island. So, if you have dual lands such as Breeding Pool, Hallowed Fountain, or any other nonbasic land that has the land type Island, you get to freeze creatures for a turn each time you play one of them. Best of all, if you happen to make all lands Islands - such as with Stormtide Leviathan or the Enchantment Prismatic Omen if you're also in Green - every land you play has that effect.
What held back Guardian of Tazeem from competitive play is that it was vying for deck space with Icefall Regent in Standard. The Regent can keep a creature tapped down as long as it's on the battlefield. While on paper the Guardian of Tazeem can tap down a lot more things, having to depend on a land-drop makes it less consistent. Also, the Regent being a Dragon made it fit better into many Dragon-centered strategies at the time.
The only competitive play that Guardian of Tazeem has seen over the years was in occasional Azorius Aggro deck lists. Even in decks that relied on staying ahead on tempo and winning the game in the air, it was still relegated to sideboard action. About the only consistent home for Guardian of Tazeem came years later in Commander, with the printing of the Sphinx tribal lord, Unesh, Criosphinx Sovereign. As Unesh makes Sphinx spells you cast cost 2 colorless mana less, pretty much every mono-blue Sphinx becomes playable in that context.
Like many creatures who have been useful but on the fringe in competitive play, Guardian of Tazeem has found its niche in Commander. The Guardian has also found a home as a tempo piece in Patron of the Moon and Meloku, the Clouded Mirror decks, which involve a lot of Islands leaving and entering play on a regular basis. As generally weak as Battle for Zendikar was as a set, the Guardian of Tazeem was far from one of its weaker cards.