NEW YORK ( TheStreet) -- As the first device to run on Google's ( GOOG) tablet-specific Honeycomb operating system, Motorola's ( MMI) Xoom, which hits shelves Thursday, is heralded as one of the few big challengers to Apple's ( AAPL) market-leading iPad. Reviews, however, which started to circulate Wednesday night, are mixed. According to preliminary tests by TheStreet, navigating around the Honeycomb OS will take some getting used to for users familiar with the first iterations of the Android smartphone platform. Apps like Gmail and Android Market look and act differently, and sometimes froze up or crashed. That said, many older Android apps seem to scale well with the Xoom, and videos look crisp, though some are a little slow to open. The Xoom is available for $600 with a two-year data contract and $800 without at Best Buy ( BBY) and Verizon ( VZ) stores. The tablets will run on Verizon's 3G network for now, and users will be able to upgrade to the carrier's faster 4G service in a few weeks by sending it back to Verizon for the (free) conversion. The Xoom features two cameras -- a 2-megapixel one on the front, a 5-megapixel one on the back -- a 10.1-inch screen and gets its power from a Tegra 2 dual-core processor from Nvidia ( NVDA). Apple's iPad, which held a 75% market share of global tablet shipments in the quarter ending in December, has had some of its share nibbled away by Android tablets, according to research firm Strategy Analytics. Android devices, which are made by a pile of manufacturers including Samsung, Motorola and Acer, accounted for 22% of shipments, up from 2.3% in the previous quarter. Tablet sales are expected to reach 54.8 million in 2011, up from 19.5 million the year before, according to Gartner. On March 2, Apple will unveil the latest version of its iPad at an event in San Francisco, which TheStreet will cover via live blog. --Written by Olivia Oran in New York. >To follow the writer on Twitter, go to http://twitter.com/Ozoran. >To submit a news tip, send an email to: firstname.lastname@example.org.