My first experience with Titan: the Arena was frustrating. The Avalon Hill representative at Gencon refused to answer my question, "Is it like Titan the boardgame?" He spent several minutes dancing around the answer, evidently unsure which answer would convince me it was worth trying. I was (and am) a Titan fan, but it didn't matter. My answer is that it has many creatures with the same name, but not much else in common. And it's a good game!
This is one of (at least) three incarnations of a Knizia concept and I think for some crowds the best. The others are Grand National Derby (a little simpler) and Galaxy: the Dark Ages (more complex). There are eight creatures (cards) in the arena. A player wins by having the most valuable bets on the three creatures still alive at the end of the game.
A player turn consists of optionally placing one of their five allowed bets on a creature, then playing a card (mandatory) and possibly using the special ability of the creature. If all creatures have a card played on them, the weakest is removed. The player then refills his hand and play passes to the next player.
The earlier a bet is placed, the more it is worth at the end; four for a first round bet, three for second, etc. Only one player is allowed to bet on a creature each round. Each player may also make one hidden bet in the first round worth five, but it takes one of that creature's cards out of play. If the player has more open points riding on a creature than any other player, he is also entitled to use the creature's special ability when he plays a power card on that creature. These special abilities allow another card play (Hydra), remove an exposed power card (Dragon), force opponent to play with half his hand for a turn (Cyclops), draw cards from opponent's hand (Titan), etc.
Each creature has eleven power cards in the deck, one each 0 through 10. There are also wild power cards from 0 to 10 also that can be played on any creature, but do not allow the special ability of the creature to be used. Only the last card played on each creature determines its strength. The previously played cards remain under the subsequently played one and occasionally they resurface due to the special abilities of the creatures. There are also some referee cards that allow the player to pick up a power card or expose all secret bets on a creature.
When all creatures have a card played on them in a round the lowest creature is removed with all of the bets and its cards are then worthless. Players can discard up to three of these each turn if desired. If there is a tie for lowest power creature, play continues until there is a single weakest creature. (This can happen by all but one of the tied creatures getting stronger cards or by one of the tied ones or another creature getting weaker.) After five rounds there are three creatures left and the bets are totalled. The player with the most points wins the contest.
It's easy to teach and newbies have a fair chance to win. One interesting facet is that you will be "partnered" with other players trying to keep some creatures alive while doing your best to eliminate their other creatures.
There are several real decisions to make in this game. For example, do I play a low card on my creature to use its special ability and plan to play a higher one later? This strategy can backfire if you don't get another turn or "have to" protect another creature on your next turn. Betting is also challenging. Should one place all bets in the early rounds to assure high points on the surviving bets or hold some until later rounds when it is likelier to survive for a smaller payout? Also, some creatures seem stronger than others, so opponents work to kill them off. It also can be very risky to place more than one bet on a single creature (in different rounds), because no one else will be concerned with its survival.
One frustration that I have heard is that when the deck runs out before the end of the game due to "overuse" of the powers of the Ranger (draw three cards) and the Warlock (discard three cards), you are stuck with worthless cards at the end. Also, sometimes it is clear that a player can't win and is reduced to a kingmaker.
All in all, I recommend this game as a light, fun filler type game. It plays in a half hour or less with experienced players and usually winds up being fairly close until the last card is played. It is also often enjoyed by "non-gamers."