Keeping rodents as pets means you encounter a lot of misconceptions. Rodents are after all a "pest" and "unclean" and they have a short lifespan, no personality and low intelligence. People assign cruel, arbitrary values to their life and make jokes they would never dream of making about a dog or cat.
One of the above is true; the majority of rodents are short-lived, something often made even shorter if your animal originates from a rodent farm, or unethical breeder or pet shop. Incorrect husbandry, such as keeping a social gerbil alone will also drastically shorten lifespan; a lonely gerbil may live up to 18 months, but if kept with company will likely reach between 3-5 years.
Within this relatively short lifespan rodents pack so much activity, life and personality that it almost makes up for the short length of time they are in your life.
It is true that some rodents smell, it is after all one of their strongest senses and a major form of communication for them. Rodent keepers learn to become accustomed to a certain level of musk and scent-marking, since this means their rodent is happier and more secure. Overzealous cleaning of cages can conversely make the problem much worse, as the rodents will scent mark obsessively to reclaim their territory. Like any animal, this varies greatly - male mice can be quite strong in scent, whereas rodents such as harvest mice and steppe lemmings have almost no odour at all.
To say they are unclean however is false, rodents groom themselves and each other frequently, it is both a form of bonding and social communication. They should never need human intervention for to wash them, although species such as Mongolian gerbils and chinchillas should have a dust bath supplied to allow them to clean their fur. Rodents are only unclean if ill, or kept in poor conditions.
Rodents exhibit a full range of behaviours, their reactions and preferences to things can differ greatly. I don't see how anyone can interact with their pet, given the correct husbandry and believe they have no personality! You should always try a full range of nests, foods, and accessories such as wheels, or climbing material for each individual since there is no telling what a particular animal will love or hate. Some rodents will adore your handling, pet mice may brux when happy, and mice pups and guinea-pigs jump vertically in excitement known as "popcorning". Some rodents can be trained to follow simple commands, take obstacles courses, and gerbils are not alone in very swiftly learning the sound of their own names.
More exotic rodents will be less interested in human interaction, and some such as the African pygmy mice are too small to handle safely. The fact that some exotics are more pets to observe than interact with is hardly a failing on their part, or indicative of a lack of intelligence. Given a natural habitat, and space and items to exhibit as full a range of behaviour as possible and it is easy to see how individual each rodent can be.
More established rodent pets can bond with an owner every bit as much as a dog or cat, and in some cases more so. Male mice and rats can be happy riding on an owners shoulders, and pet flying squirrels can bond very closely with an owner providing they have good breeding and are acquired at a young age. The important aspect is to consider what you want from a pet, for a rodent can be every bit as rewarding as a larger animal - it just may need a keener eye to see it.
