2007-2011 was the ratings peak for TNA. The numbers went down in 2012/2013, the last big audience they drew was October 2011 when they drew over 2 million viewers for a show (it was either a 1.3 or 1.4 rating). By 2 years later they'd pissed half that audience away and were averaging a little over a million viewers.
My favorite year of TNA in the last 7-8 years was 2009. That year also received TNA's highest consistent ratings ever, there was a stretch during the summer where they got 1.3 every week. The Main Event Mafia was a really strong stable unlike the garbage ones that followed (Aces & 8's, the Beat Down Clan, Immortal). There was a purpose to the stable, it had star power, and the ongoing story made for entertaining television. The ending of the year also had the fantastic Desmond Wolfe/Kurt Angle feud and great AJ Styles title win, and that latter part of the year is the only time Russo solely had creative power in TNA. Hogan and Bischoff coming in changed the entire direction of the company.
2010 was pretty hit and miss, but the highs and even the clusterfucks were more entertaining than anything TNA have recently done. I thought the initial part of the 'They' storyline was pretty good. The 'They' reveal episode of Impact drew a 1.4, and it featured a 40 minute opening talking segment. Early 2011 was pretty good but by the summer wasn't that great. Too many Mr. Anderson face/heel turns, same goes for Kurt Angle.
2012 and 2013 were hit and miss. Aries' title reign was totally botched, his character became a kiss ass bitch when he was champion, and his match with Jeff Hardy at Bound For Glory had a totally flat build since they were both faces. The only feud with any heat from 2012 was Roode/Storm. The ratings started to go down during this period as well. Too many gimmicks like Open Fight Night, Gut Check, and the Bound For Glory Series but not enough feuds/storylines with heat.
2013 at first had some interesting stuff with Hogan/Bully Ray but as the Aces & 8's members continued to be revealed the product got worse, as it was basically the nWo Job Squad + Team 3D. The product improved later in the year though once new characters like EC3, Spud, and Samuel Shaw were introduced. MVP's initial entrance into TNA was entertaining, Eric Young's title reign sucked (a Gaburick decision), and Bobby Lashley's title win and forming a stable with MVP and Kenny King (a Russo idea) was great. The product seemed to lose its footing after Bully Ray put Dixie through the table. Recently they turned Lashley face when he was having the best run of his career as a heel, and they had MVP form a meh stable.