Seasons 1 and 2 are pretty good and enjoyable, seasons 3 and 4 are abysmal.
During 1 and 2 -the show wasn't 'realistic' per se but it was 'grounded'; with 3 and 4 came slow motion matrix gun play and long drawn out fire fights.
In 3 and 4 they wrote their characters to exude 'convenient' ineptitude, stupidity and incompetence - like "intelligence" officers wondering off unarmed in hostile territory for no apparent reason or Stockholm syndrome that takes minutes to develop.
Also why did they insist on showing us how bad ass red troop is by portraying irregular combatants like Al qaeda as some super bad asses themselves just so red troop could come in beat them like they are 'The chosen ones' or something?
They sort of made police SWAT (SO15/19) and blue troop 'red shirts'.