Actually you can work as a hospitalist and work like 14 shifts a month...thats like half the month off. With an average salary of about ~180,000, the pay is below the average physician salary, but since you don't have your own panel of patients, you truly are off for 2 weeks a month.
General outpatient IM really depends on the specific practice, in terms of both money and lifestyle. The average income is about ~150,000 but in a large practice, call can be fairly minimal. Also, the nature of call isn't always all that strenous with the advent of hospitalists to take care of inpatient issues.
In terms of the subspecialties, your lifestyle depends on the field. In general, fields like cardiology will require hours similar to that of a fellow, although not always. The reimbursement is terrific though. Other fields like endocrine and rheumatology make for a more 9-5 kind of lifestyle with very limited call. These specialists also make a lot less though (<200,000 typically). Critical care is a subspecialty that allows for shift work too (typically 2 weeks a month for like ~200,000).
As an IM applicant, I actually haven't met a generalist or specialist who regrets their career choice, although I'm sure theyr'e out there, as is true in other fields as well. In most cases, your lifestyle will be a lot more controllable than as a resident, and certainly more so than your general surgery colleagues.
That being said, most of the surgeons I've met would rather give up their left nipple than do IM and most IM folks can't stand the work that radiologists do even if it means longer hours and lower reimbursement...so do what you enjoy.