It's hard to really say much just from looking at a screenshot. When multiple previous techs lead to a tech, is that and and-requirement ("Construction requires Horseback Riding and Masonry") or an or-requirement ("Construction requires Horseback Riding or Masonry")? On the whole I liked that Civ4 allowed both (Rocketry requires Artillery or Flight; there also were and-requirements for some techs that showed up in the upper-right corner of the tech on the tree).
The boosts ("eurekas"? that's a synonym for it?) seem like a good idea, although I agree that most of them sound pretty easy. However, it's not clear from the screenshots what the effects of them are. I know they've talked about civilizations near the coast being better at sailing-related stuff, which makes sense and sounds fun, but how fun will depend on the effects.
Edit: As for length... I don't know what the tally is for Civ4 off the top of my head, but Civ3 has 83 techs with the latest patch. So while 68 is somewhat lower, if you count both, which seems fair since the civics effects would've been integrated in Civ3/Civ4, that's 118 and considerably more techs. Thus in number of techs, it seems like more than enough from vanilla. I know some people like mods with greatly expanded tech trees, but to be honest I've found the defaults in III and IV to be a pretty good starting place, and never do wind up finishing games with the larger mods enabled.
The pacing could still be another issue. I think Lemon's right to call out that the number of turns seems low - even if in that screenshot the civ being played has very high science for that 4 turns for writing, Nuclear Fusion only takes 10 times as long to research as Archery. By comparison, in Civ III, Nuclear Fission costs 280 tech points (prior to adjustment for map size, etc.), versus 3 for Warrior Code (Archery) or 8 for Writing. Taking the closest case of flip-flopping archery and writing and taking Fission as being as complex as Fusion, we're looking at 3.5 times more difference in tech cost in CivIII... which suggests that the science rate will increase more slowly over time in Civ5. Part of this could be lower bonuses for buildings such as Libraries and Universities, but some of it could also be smaller maps/fewer cities. I'm hoping the latter is not the case as much as Civ5 in particular, as Civ5 lost that ruling-a-large-empire feeling that I enjoyed so much in Civ3 (and to a lesser but still acceptable extent in Civ4).
Alternately, the techs could fly by super-quickly towards the end, which would arguably be more of a pacing issue than having science increase more slowly. In the end though, it's hard to really tell without playing. I can compare numbers to earlier Civ versions, but I can't account for new features that could make the new numbers play out well (or not) in practice.
I don't have the tech cost numbers for Civ4 off the top of my head, but they felt largely similar to Civ3 when playing. Of course if they are widely different than Civ3 in practice, that would show even more that comparing them for Civ6 is an exercise in futility.
