The familiar Serious Sam shooting at diverse enemies is hurt by cartoony 2D backgrounds and Sam getting lost in battles
According to the storyline, "Serious" Sam Stone must travel back in time to defeat Mental's monsters and save the future of humanity. However, this time Mental is not really running things. It is General Maxilla who prepares Serious Sam's enemies for battle. The game is similar to previous Serious Sam games in that there are many diverse enemies for Sam to fight at once with a variation of weapons to use.
One major difference between Serious Sam: Double D and previous Serious Sam games is the fact Serious Sam: Double D use the Gun Stacker, a device that allows Sam to connect weapons and fire them at the same time. Sam can actually have numerous combinations of connected weapons. Therefore, Sam can switch from one combination of connected weapons to another in the heat of battle. There is a Porta Pad, a portable jump pad that Sam can use to reach otherwise unreachable areas.
The eighteen levels cover various settings from Ancient Egypt to Pompeii. Each level features many secrets. They also contain special challenges you can pick up so you can play these challenges away from the main game. One problem I found is when Sam battles many large enemies at once. I had a tendency to lose Sam among the large enemies because he looks so diminutive. The developers could have done a better job making Sam more visible on the screen. This flaw makes the battles unnecessarily more difficult.
The graphics are not that good but that's partly because it's 2D. However, the graphics are quite cartoony. Sometimes the background can get covered up by Sam piling up so many bodies from the kills. The piling up can sometimes be necessary in order to move on without falling into a pit of spikes or getting burned by lava. The monsters range from the familiar to the preposterous. There are Gnaar and Kleer skeletons but there are also Vuvuzelators that carry Vuvuzelas to attack Sam. There are ridiculous bosses such as gigantic hamsters and a 20 foot tall female who sends Femikazes (female version of Kamikazes) to blow up in front of Sam.
Serious Sam: Double D can be some fun for Serious Sam fans, but I don't think it would fully satisfy them. It can temporarily entertain them while they wait for Serious Sam 3: BFE.