Though the Soldier is no doubt one of the best classes for combat, remember that he cannot use the more powerful biotic and tech abilities that the other classes have the luxury of using. No biotic and tech abilities means other classes have more choices as to how they want to deal with their enemies - they can stun, throw, or lift them, shatter their shields or destroy their weapons. They are better at healing their squad, increasing their shields, opening difficult crates and lockers that contain nice loot, and repairing your vehicle, the Mako.
Some doors can only be accessed if you have a high Decryption talent, which the Soldier unfortuantely can not reach. Some important items and side quests can only be obtained if someone in your squad has a high level of Electronics, a tech talent that allows you to open objects scattered throughout the planets you visit. If you choose to go with Soldier, make sure to at least bring a squad member with tech talents wherever you go.
Playing Mass Effect with the Soldier class is attractive because of the hundreds of weapons you will find throughout the game- from completed missions, dead enemies, storage, hidden areas, and shops. You will realize once you become a Spectre and are given freedom to go where ever you want, that there are plenty of great weapons planted throughout the places you visit, in underground caverns, cities, etc. This lifts the burden of knowing you don't have to make tons of money to buy the best supplies from the shops.
Other classes can't enjoy the same adventure when they pick up weapons and realize they can't use to its full potential. The looting experience is an enjoyable one for the Soldier. It means more fun exploring the world as well as blasting enemies into dust with those powerful assault rifles and shotguns you get.