Okay, maybe there are C-15s that the angry beavers / drunken monkeys didn't work on. Fine. Maybe there are some examples out there which run acceptably. Fine.
However, the C-15s are made from mostly used M16 & M16A1 parts that are refinished (to varying degrees), and slapped onto new AR-15 lowers. They have a 1:9 twist bbl, made by anyone's guess, of unspecified steel. They're $625 from J&G, plus shipping, plus dealer transfer fee.
S&W just introduced their new M&P-15 Sport. Yes, it lacks a dust cover & forward assist, but it does have an extended brass deflector. It also has a 1:8 twist 5R rifled bbl. made in house (in house as in probably T/C who S&W owns) from 4140 steel. The new BCG has been MPI. Every part on the rifle is new. They sell for $600 at the big box stores - no shipping, no transfer fees.
You can also go with DPMS if you like, and get the Panther Sportical which lacks the dustcover & forward assist, or the Panther Oracle with its conventional M4 / A4 (or A3 as they call it) upper. These both have light contour, conventionally rifled, unlined, 1:9 twist bbls; which are made in house from 4140 steel. They don't have MPI BCGs. Again both do have all new parts. These rifles have MSRPs of $715 & $705, respectively, which is essentially equal to the M&P Sport's MSRP of $699.99 - other members here report street prices in the very low $600 range, as expected.
In conclusion - even if every Century C-15 was well finished, and every C-15 ran perfectly - why would anyone pay more money for a rifle full of used parts & new parts of unknown quality; than he or she could get a completely new rifle for - made with parts of known materials & manufacture?