Simply, they are saying that the vehicle value ($1550) is not worth the higher cost of fixing it ($1900).
Some random thoughts....
1) Make a list of all the POSITIVES and optional equipment that the vehicle has. Has the vehicle recently had major repairs done to it (that would affect the value)?? Does the vehicle have an 'upgrade' stereo, low mileage, sunroof, automatic, etc. that may not have been considered when value was set?? Make sure that the insurance company considers ALL the facts that might affect the value.
2) Make sure that the insurance company includes sales tax and tags in determining the total compensation.
3) Check the current classifieds, car value books, etc. to determine what the 'comparable' car is selling for in your area. Some good sources are:
http://www.kbb.com/
http://www.autosite.com/
http://www.edmunds.com/
http://www.nada.com/
Only you can determine how much the car is worth. If it is a rolling wreck with a shot engine and no A/C, then it might be worth the offer. One telling thing to consider..... are you going to take the money that they offer and FIX your car, or are you just going to get a 'new' one??
Finally, if you don't agree with their offer, you can always refuse and try to negotiate a higher one. And failing that, you can file in Small Claims court. If you do decide to file, realize that you will very probably be arguing against an attorney (provided by the insurance company).