An excellent game through and through.
Controls:
A fairly standard RTS game interface the player can quickly get the hang of. A comprehensive tutorial explains everything the player needs to know without dragging on for too long or overcomplicating things.
The map is kept simple and informative and does not confuse despite the game being in 3D. Issuing orders (e.g. move to destination) can be tricky due to the perspective but this generally poses no problem. (I recall the game being pausable allowing the player to correct any misconception the AI might have as to its orders, but I may confuse the game with another on this point)
Single-player campaign:
A consistent linear campaign that is neither too short nor too long and features a variety of mission types to keep the player interested and on their toes. Assets, i.e. the fleet, research and upgrades and resources carry over between missions, making the game more interesting as the player has more of an incentive to look after their ships.
The campaign can be very challenging and - for me - remains so throughout. The player does not 'outgrow' the game half way through and simply walk through to the end. And while no difficulty setting is available, the game adapts to the player's fleet strength at the start of a mission by giving more or fewer assets to the enemy. Hence the player is given a fair chance to prevail, whether he came out of the last mission with an armada or a crippled handful of ships.
Multiplayer:
The game features online multiplayer as well as the usual 'free game' against AIs of varying difficulty levels. With a range of options these offer more variety in the game besides its campaign and can be very entertaining indeed.
Gameplay:
Combat is loosely based on the 'rock paper scissors' mechanic as different ship types are vulnerable or strong against others. Individual units cannot be customised; instead the player decides which ship types to build in order to create a fleet that is best suited to the situation.
Individual battles can also be quite gripping. Rather than giving all ships a single order to attack and watch the fireworks, the player must direct their fleet and manage it throughout the engagement, if they want to win. This might involve directing different ship classes againts the target they are strongest against or withdrawing or repositioning ships when they in turn are targeted.
Besides combat there are a number of other aspects demanding the player's attention. Exploration is quite important as the 3D map with fog of war leaves a lot of hiding spaces to the enemy, if neglected. There are resource veins to be monitored, enemy fleets to be tracked and - of course - the own armada to be hidden and ambushes to be prepared.
Research is another interesting aspect. Beside the passive research that improves ships or makes new ships available for construction, capital ships can be customised by attaching modules with differnt functions to them. As each ship has only a limited number of module slots, the player has to choose how to upgrade an individual ship (e.g. a carrier or a battle cruiser) to best suit their needs. For example, one ship might be fitted with a jump module allowing it and nearby vessels to jump to the other side of the map, while another is fitted with a sensor array intead, that allows it to detect approaching enemies from afar.
Overall the player is given many choices without being forced into eternal micromanagment. Different strategies can be evolved and tested. Perhaps a surprise attack jumping right into the enemy shipyards will work? Harrassment with small and fast ships might draw part of their fleet out into the open, only to find a cloaked battlecruiser waiting. There are many poossiblities open, and it is great fun to experiment, be it on the AI, or on other players.
A post scriptum about the graphics:
The game is very presentable indeed, giving a realistic theme to the game and successfully avoids that certain cheesieness some games bring upon themselves.
Unless you count among those obsessed with the latest graphics games have to offer, you will certainly not suffer looking at Homeworld 2. Animations are very detailed and are quite charming, assuming it's not your ship that is blowing up. Firefights in particular are very picturesque with plenty of fireworks. Personally I am always reminded of some of the combat sequences in Battlestar Galactica (the 'recent' one); small fighter craft and corvettes chase each other while the battle itself is dominated by the huge and slow-moving warships as they try to crack each other open with beams and gun batteries.