NEW YORK (TheStreet) -- Investors might want to exert at least a little bit of caution when it comes to King Digital (KING) stock for now, despite the strong results that the game maker reported late Thursday for the fourth quarter.

For one thing, King had unusually strong successes with its game launches last year, including the recent Candy Crush Soda Saga, said Wedbush Securities analyst Michael Pachter in a research note Friday. "We think it is prudent to model only moderate success this year," he said.

Meanwhile, King's older (and still most-popular) game, Candy Crush Saga, has shown signs of weakness in the past year or so. The game's popularity peaked in mid-2013, but it still represents 45% of King's bookings, said Mark Mahaney, an analyst at Royal Bank of Canada (RY - Get Report) division RBC Capital Markets, in a research note.

King is expanding beyond casual games into markets including mid-core gaming -- titles that fall in between the traditional casual and core gaming segments. That was underscored in its planned second studio purchase, said Pachter. King disclosed while reporting fourth-quarter results that it had signed a deal to buy Seattle-based game developer Z2Live for up to $150 million in cash. Z2 will be King's first game studio in the U.S. "In our opinion, this deal makes strategic sense but also carries operational risk," said Mahaney.

Z2 makes freemium online action and strategy games -- titles that are free to play up front, but charge for upgrades -- including Battle Nations and MetalStorm. "King has no history of success with these games," said Pachter. But he said: "We think that its cross-promotional ability and its disciplined approach to game development position it to thrive with its first entries, expected later this year."

Pachter was encouraged by King's plans to expand beyond its comfort zone of casual games, he said. But he lowered his estimates for King's 2015 results, reflecting the company's release schedule, which is heavily weighted to the later part of this fiscal year, he said. Pachter now expects King to report revenue of $2.3 billion for fiscal 2015, down from his earlier estimate of $2.6 billion.

The higher-risk investment in new game categories and lack of visibility into the longevity of King titles outside of Candy Crush Saga were among areas of concern cited by J.P. Morgan analyst Doug Anmuth in a research note Friday. Cannibalization of the core Candy Crush game by Candy Crush Soda Saga was less-than-expected in the fourth quarter, but Soda impacted other King games, suggesting weakness in games like Farm Heroes Saga, the Bubble Witch Saga and Pet Rescue Saga, he said.

Anmuth and Sterne Agee analyst Arvind Bhatia remained "neutral" on King stock, while Pachter and BMO Capital Markets analyst Edward Williams each maintained an outperform rating, and Mahaney maintained a market perform rating.

"Investors should not be overly optimistic on the stock, even though it looks cheap on [the] surface," said Bhatia in a research note Friday. He cited Soda's cannibalization of other King titles, and a projected slight decline in revenue and drop in EBITDA margins this fiscal year. King management had also been overly conservative with the results forecast for this year and finished better than that estimate, he said.

King's fourth-quarter revenue slipped to $545.6 million from $601.7 million a year earlier, while profit fell to $140.6 million, or 44 cents a share, from $159.2 million, or 50 cents a share. But for the year, revenue grew to $2.3 billion from $1.9 billion, while profit increased to $574.9 million, or $1.79 a share, from $567.6 million, or 41.75 a share.

King shares were up 14 percent at $16.81 at 12:54 p.m. Friday.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.