Alastair has written an excellent article on the historic Protestant affirmation of the real presence of Christ in the Eucharist, here
. It's well worth your time. Below are a few excerpts from near the end where he provides some helpful evaluations and suggestions.
"The Reformed doctrine, through its wish to avoid certain of the dangers perceived in the notions of transubstantiation and local presence, and rather subtle distinctions and definitions, can open itself up to suspicions of evasion and equivocity, suspicions that in some cases may be well founded, especially among the Reformed of later generations. However, as one examines people such as Calvin more closely, one finds that many of one’s suspicions and objections are satisfactorily addressed. This is not to say that the Reformed always express their doctrine of the Supper in the most appropriate or unambiguous of ways, or that one couldn’t improve upon it by using stronger and more robustly affirmative expressions, but the wiggle room isn’t as large as some may suppose. Unfortunately, when one’s affirmations are so hedged with necessary qualifications and denials, they can lose some of their force and invite questions in the hearers. One sometimes wishes that Reformed theologians had adopted more positive and assertive formulations for their doctrine from the start. As it was, the weight of the Reformed Eucharistic doctrine shifted rather steadily away from the affirmations to the denials and qualifications.
For all of its strengths, for instance, the accent of Calvin’s doctrine frequently lies in the wrong place, in a manner that will dissatisfy many. Calvin places entirely too great a focus upon the way that the Supper communicates to our minds, inviting the notion that the efficacy of the Supper is entirely mediated by our mental faculties, perhaps sowing the seeds for serious declension in later Reformed doctrines of the Eucharist, and inviting the suspicion (such as that of the Lutherans in the Formula of Concord) that for the Reformed the Supper communicates nothing, but merely triggers our remembrance and faith to enjoy a communion with Christ that occurs unmediated by the sacrament. With Calvin’s focus upon the mind, the ‘rite-ness’ of the Supper is easily lost sight of and the Supper becomes a matter for spiritual contemplation, primarily existing to be meditated upon, rather than eaten. It also invites a subjectivizing and interiorizing movement in our understanding of the sacrament. God’s work in the sacrament can be downplayed, with the accent being placed upon our work of raising our thoughts to heaven, remembering Christ’s death, and grasping him by faith. At points this growing stress upon our action in the sacrament threatens to displace the primacy of God’s action within it. It is worth remembering that the medieval Mass that Calvin was reacting against was also for most a spectacle to be meditated upon: in this respect, Calvin’s doctrine could be accused of not making a sufficient break with the abuses of the past..."
"While I find his precise articulation of the doctrine of the Eucharist unsatisfactory, largely on account of certain misplaced accents and lacunae, I believe that Calvin presents the most promising and fertile framework for addressing some of the issues relating both to the question of Christ’s presence in the Supper, and of our participation in his flesh and blood. To my mind, the key strength of Calvin’s proposed approach lies in its robustly personal character. Calvin’s approach provides a clearer way for us to understand the Eucharist as fundamentally Christ’s personal action. Throughout the Eucharist Christ is personally active, not merely passively present, but actively communicating himself. This leads to a further point: Christ’s personal self-communication through the work of his Spirit provides a way for us to focus less upon the elements as static presence, and more upon Christ’s presence as something inextricable from the action of the sacrament. Finally, in what is perhaps his most daring move, Calvin speaks of the Spirit lifting us up to Christ’s presence, rather than Christ being dragged down. What this suggests is that the mystery of the Eucharist is not primarily something that happens to bread and wine, but something that pertains to the entire rite, both elements and communicants. This extension of the mystery enables us to overcome what Peter Leithart has termed the static ‘zoom lens’ with which element-focused approaches to the Eucharist approach the rite. In the place of this we have a ‘wide-angle lens’, which comprehends the entire rite and all participants in it. As Douglas Farrow has observed, Calvin’s focus on the work of the Spirit also opens the possibility of a more eschatological cast to our doctrine of the Eucharist. If the Spirit can unite things distant in space, surely he can also unite things distant in time. Calvin’s approach provides an opening for us to think of the Supper as an anticipatory enjoyment of the life of the kingdom in the present through the work of the eschatological Spirit. It is in these areas, I believe that the promise of the Reformed doctrine of the Eucharist is to be found."