Fans of struggling teams so often pin their hopes of a quick turnaround in the franchise's fortunes a new star under center (which is understandable as no player in team sports has a bigger impact on a team's success than a QB has on an NFL team) but no matter how great you feel in April it is worth noting that it is a real gamble every time.
Of the 30 QBs drafted over the past 10 seasons (not counting last season as it's too early to judge - though it looks promising so far) more than half look 'disappointing' (this classification varying between complete busts to just failing to turn into at least a quality starter which is the minimum you might expect from a first round pick), the next biggest tranche are QBs who look 'OK' (i.e. starters but they wouldn't be considered a (potential) franchise QB and they could certainly be upgraded) and only 6 (or 20%) look like being (potential) franchise QBs.
Still after a long period where there have been a lot more disappointments than successes at least it looks as though we are starting to see a new crop of good QBs and QB prospects coming into the league as most of the best looking QBs have been drafted in the last few years.
As an aside, things don't get a lot better when you slide down a round - 10 QBs have been taken in the second round over the same period and it evens out to being around 5 disappointments and 5 OK players (with Derek Carr still looking like potentially being capable of taking the next step).