Dungeons and Dragons Miniatures is a skirmish-level combat game of man-to-man, man-to-monster and monster-to-monster combat. Thematically it's inspired by the Dungeons & Dragons universe and most game mechanic revolve around the rolling of a 20-sided die.
I came to the game system late, just as it was extensively revised from the original system (listed separately on Boardgame Geek's database) into what's known as the Second Edition. Interestingly, not long after making this major revision Wizards of the Coast decided to discontinue the game as a stand-alone miniatures game and make all future miniatures just for the role-playing game. Evidently the newest edition of the RPG plays much like the 2nd Ed. minis and it may have seemed to duplicate the product. The stat cards for the miniatures include data for use in the RPG, so the miniatures can do double duty as RPG tools or boardgame pieces.
The revised game is actually a little less wargame-like than the original rules, which included commanders and morale effects, but there's still considerable scope for tactics.
The game is ruthlessly small scale, with an upper limit on the number of characters on a side of 10. While artificial, it does keep the game system from degenerating by having a single powerful piece being overwhelmed by hordes of small weak pieces.
Each character has a point value used for army-building and victory conditions and an alignment of either good, evil or neutral. In the earlier version of the game the alignments were further broken down between chaotic and lawful modifiers so a creature could be Lawful Evil or Chaotic Good for example. In the new games most creatures are just plain "neutral." A fairly large number are characterized as "evil" while only a select few are "good." Good and evil characters cannot co-exist in the same warband and some game effects and powers can be affected by alignment.
Each character belongs to one of more of the four "factions" which are borderlands, civilization, the wild and the underdark. All the creatures in a given warband must share at least one faction in common, which helps provide some thematic coherence to the warbands.
Each character has a level, which can have some game effects and an armor class and a defense value. Armor class is generally used against most normal attacks while the defense value is often used to defend against special kinds of attacks such as magic or psionics. The defense value can be further modified into sub categories such as reflex or willpower when faced with particular kinds of attacks.
Every kind of attack, whether physical, magical, psionic or poisonous is resolved in the same way, which is a real strength of the game system. The attacking player rolls a 20-sides die and adds the creatures relevant attack value plus any modifiers to the result. If it equals or exceeds the relevant protecting value (armor class or defense value plus any modifiers) then the attack succeeds and inflicts the effects stated on the attackers card. These effects generally include a number of hit points but often include other effects as well. The number of hit points a creature has is listed on the data card.
Also listed on the card is a speed value, which may have an "F" denoting a flying creature. The main body of the card contains an illustration of the character, its attack actions, any keyword abilities (such as alignment, race and other common status) and any special powers.
Everything is listed on the card and a player will rarely have more than 10 creatures and their associated cards to track, so the workload isn't too bad. I've found that the game is easily teachable to fairly young players.
The cards from the older versions of the game are not compatible with the news system but WOTC is publishing online revised cards for all the previously produced miniatures that can be downloaded and printed out at home, so no creatures have been made obsolete.
For the historically oriented wargamer there's little of interest in D&D miniatures. The game play is heavily influenced by the magic-heavy D&D gaming universe where mages are as common as white-collar professionals in our world. (In contrast to the Tolkien world of Lord of the Ring: TMG where wizards are powerful and extremely rare).
That said, it is a well-designed, easy-to-play skirmish level wargame that involves real tactical choices and may provide a bridge game between fantasy-oriented RPGers and board wargamers.
As a discontinued collectible game it may be possible to pick up all the common you need off of eBay economically but rares, especially certain desirable ones, will probably command premium prices for a while. I wouldn't expect big discounts because the miniatures are also usable in any fantasy RPG and therefore probably won't end up in bargain bins.